Concrete Calculator — Volume, Bags and What You Actually Order
On this page
Calculate
This selector governs every field, label, result and export here and takes priority over the site header switch. Switching converts what you entered rather than reinterpreting it, so 10 ft becomes 3.048 m and returns to exactly 10.
The Pour
Choose this first. It decides which dimensions are asked for and which term each one feeds, because a slab, a footing and a wall run through the same equation with different measurements in different places.
Leave empty for one. Four identical footings is four times the volume, and this is the only place on this page where a quantity multiplier is the right move.
How It Is Supplied
It decides whether the bag yield question applies at all. Not decided is an answer: it returns both routes side by side with the bag count at all four US sizes.
It covers an uneven subgrade, spillage during mixing and over excavation, and it applies to a truck delivery exactly as it applies to bags. None is a valid answer rather than a blank one.
Your Supplier's Figures, All Optional
Overview
Every concrete calculator returns the volume. A ten by ten slab at four inches is 33.3 cubic feet, which is 1.23 cubic yards, and every one of them gets that right.
Nobody orders 1.23 cubic yards.
Two corrections stand between the arithmetic and the order, and the field runs them together into a single waste percentage. They are different things.
The waste factor is a volume correction. The hole is bigger than the drawing: the subgrade is uneven, the forms deflect, the excavation went deep in places, concrete is spilled. Published guidance puts it at five to ten percent and it applies to a truck delivery exactly as it applies to bags, because the hole does not care how the concrete arrived.
The bag yield is a materials question and it exists only on bags. An eighty pound bag yields 0.60 cubic feet, from a compacted density of 133 pounds per cubic foot on the manufacturer data sheet. That is the figure to order by, because a form holds plastic concrete.
The same data sheet lists a cured unit weight of about 140 pounds per cubic foot, which works out at 0.57 cubic feet for the same bag. That figure circulates elsewhere as a real world yield and it is not a loss: it is what the bag becomes after it has consolidated, and it answers a different question from the one a bag count asks.
This page reports the corrections separately, because one of them disappears the moment you order a truck, and it orders by the plastic yield while explaining where the other figure comes from.
What to Look at First
Read the order before the volume. The volume is the figure every calculator returns and this one returns the same number; the order is the figure you act on, and on bags it is a count at the ordering yield while on a truck it is a calculated need pushed up by an increment and a minimum. The mixing labour on its own line is the third thing to read, because it appears on no price and it decides the bags against ready mix question for most people.
How to Use This Calculator
Choose the pour type first. It decides which dimensions are asked for and which term each one feeds, because a slab, a footing and a wall run through the same equation with different measurements in different places.
Enter the dimensions the type asks for. On a round pour enter the diameter, not the radius: taking one for the other is out by a factor of four and is the commonest error on the subject.
On steps, say what kind of flight it is before entering anything. This page models a solid formed flight as a stack of prisms. Open risers, a landing, and steps poured over fill are different volumes and the page stops rather than guessing.
Say how the concrete will be supplied. Bags, ready mix, or not decided. That decides whether the bag yield question applies at all.
Choose a waste factor, or none if you want the theoretical volume. Five percent suits a good subgrade and tight forms, ten percent is the usual allowance, and none is a valid answer rather than a blank.
Read the order rather than the volume. On bags that is the count at the ordering yield. On ready mix it is the calculated need, then the increment, then the minimum, with the final order quantity last, and the mixing labour on its own line because forty five bags is an afternoon rather than a purchase.
Inputs & Outputs
Inputs
Outputs
Concrete Volume Formula
Four of the five pour types run through one equation with different dimensions in different terms, so the mapping is stated rather than assumed. All lengths are canonical in feet internally.
Rectangular volume
vol_cf = len_ft * wid_ft * thick_ft
Round volume
vol_cf = 3.14159 * (dia_ft / 2) ^ 2 * depth_ft
Solid step flight volume
vol_cf = wid_ft * run_ft * rise_ft * step_sum
Step summation term
step_sum = step_count * (step_count + 1) / 2
Inches to feet, applied at entry
thick_ft = thick_in / 12
Multiple identical pours
vol_total_cf = vol_cf * pour_count
Cubic yards
vol_cy = vol_total_cf / 27
Volume with waste
vol_order_cf = vol_total_cf * (1 + waste_pct / 100)
Bag count at the ordering yield
bags = vol_order_cf / bag_yield_cf
Bags per cubic yard at a stated yield
bags_per_cy = 27 / bag_yield_cf
Bag yield from a density
bag_yield_cf = bag_weight_lb / density_pcf
The mapping by pour type. A slab uses length, width and thickness. A footing uses length, width, and depth in place of thickness. A wall uses length, the height in place of width, and thickness. A round pour uses the diameter and the depth on its own equation. A solid step flight uses width, run, rise and count.
Thicknesses, depths and rises are entered in inches and converted to feet before any volume equation runs. Lengths, widths, heights, diameters and runs are entered in feet. Doing the conversion at entry rather than inside each equation is what keeps a depth of three from being read as three inches in one place and three feet in another.
The bag yield is a density calculation rather than a measured volume, which is why the derivation is shown: an eighty pound bag divided by a compacted density of 133 pounds per cubic foot is 0.6015 cubic feet. That is where the 0.60 comes from, and it is a manufacturer figure rather than a table somebody assembled.
What a Concrete Volume Calculation Actually Answers
A concrete volume calculation turns dimensions into a quantity to buy. The arithmetic is simple and it is not the hard part.
The hard part is that the quantity to buy is not the quantity the arithmetic gives, and the reasons are not one reason.
A form is never exactly the shape on the drawing. Subgrade is uneven, excavation overruns, forms bow under the weight of wet concrete, and some of it ends up on the ground. That is a volume question and it applies however the concrete arrives.
A bag is not a unit of volume. It is a unit of dry weight, and how much concrete it makes depends on which density you measure at. Plastic concrete going into a form is less dense than the same concrete once it has cured and consolidated, so a single bag has two published yields depending on which question is being asked.
And a delivery is not a quantity either. It is an order, placed in a supplier's increments, above a supplier's minimum, with a fee below a threshold.
Between the dimensions and the delivery ticket sit three different kinds of question, and most calculators answer only the first.
The Volume Is Not the Answer, and Every Calculator Stops There
A ten by ten slab at four inches is 33.3 cubic feet, or 1.23 cubic yards. Every concrete calculator on the internet returns that figure and every one of them is right.
Nobody orders 1.23 cubic yards.
Between the calculated volume and the delivery ticket there are two corrections, and the field runs them together into a single waste percentage. They are not the same thing.
The waste factor is a volume correction. The hole is bigger than the drawing: the subgrade is uneven, the forms deflect, the excavation went deep in places, and concrete is spilled. Published guidance puts it at five to ten percent and names those causes. It applies to a truck delivery exactly as it applies to bags, because the hole does not care how the concrete arrived.
The bag yield is a materials correction and it exists only on bags. It is not about the hole at all; it is about how much mixed concrete comes out of a bag.
A reader given one combined number cannot tell which part of it goes away when they decide to order a truck instead. That is the whole reason this page reports them apart.
Where the Two Bag Yields Come From
Every calculator divides by 0.60 cubic feet for an eighty pound bag. That number is correct and it is the manufacturer's, published by Quikrete and matched by Sakrete under ASTM C387.
It is a density calculation rather than a measured volume: eighty pounds divided by a compacted density of 133 pounds per cubic foot is 0.6015 cubic feet. That is where the 0.60 comes from, and the derivation is shown here so a reader can check it rather than take it.
The same data sheet lists a cured unit weight of about 140 pounds per cubic foot. Eighty divided by 140 is 0.5714 cubic feet, which is where the 0.56 to 0.58 figure in circulation comes from.
Those are the same bag at two points in its life, plastic and cured. It is not a mixing loss and it is not waste. You order to fill a form, a form holds plastic concrete, and the plastic yield is the figure to order by.
Run both through the arithmetic and the difference is visible. At 0.60 a cubic yard takes 45 bags, which is the figure the entire field quotes. At 0.57 it takes 47.4, which is a cured volume comparison rather than an ordering figure.
On the reference slab with ten percent waste that is 61.1 bags against 64.3. This page reports the first as the order, offers the second as an explanation, and applies neither to the sixty, fifty and forty pound products, because their cured unit weights have not been confirmed and scaling a density ratio across a product list is an inference the source does not make.
A Concrete Stair Is a Stack, Not a Wedge
Steps are the pour type most calculators either omit or handle without saying what they modelled.
A solid concrete flight is a stack of rectangular prisms. The top step is one rise deep, the next is two rises deep, and the bottom is n rises deep, so the total depth is n times n plus one over two rises.
On a five step flight four feet wide, with a one foot run and a seven inch rise, that is 35.0 cubic feet.
Treat the same envelope as a triangular wedge, which is what an unformed earth slope would be, and it is 29.2 cubic feet. About twenty percent less, for a stair of exactly the same dimensions.
Neither number is wrong. They describe different objects, and a calculator that returns one without saying which has left the reader to discover the difference when the truck runs out.
This page models the solid stack and says so, and it stops rather than guessing where the flight has open risers, a landing, or fill beneath it. Those are real and common, they are different volumes, and pretending otherwise is how a twenty percent error gets shipped as a feature.
One Number on This Page Costs Strength Rather Than Money
Everything else here is an ordering question. Order too little and you make a second trip. Order too much and you have paid for concrete you tipped in a corner.
Water is different. Published guidance states that an eighty pound bag needs about 3.8 quarts, and that one extra quart can cut strength by up to forty percent. Another published source advises starting with three quarts and adding as needed, and puts the loss from excess water at thirty to fifty percent.
That belongs on a volume calculator because of when it happens. A person counts bags, buys them, opens the first one, and the next decision they make is how much water goes in. Nothing between the bag count and the mixer will tell them, and the consequence is invisible: the concrete looks the same, pours more easily, and is weaker.
Two things keep it honest here. The figure is for the eighty pound bag and this page does not scale it to the others, which carry their own on the bag. And the rounded bag count is a purchase count, not an instruction to mix everything bought, so the water total is for the bags actually going into the mixer.
Why This Page Has No Verdict
The plumbing calculators on this site test a figure against a published code minimum and return a pass or a fail, because plumbing codes publish minimums. Concrete volume has no equivalent. There is no table, no edition and no threshold.
What follows is that this page returns a quantity and names its own limits rather than pretending to authority it does not have.
It does not know whether the slab is thick enough, what strength class the job needs, what reinforcement goes in it, or whether the thing being poured should be poured at all. Those are mix design and structural design, and for permitted structural work, foundations, retaining walls and commercial projects they belong to a licensed engineer, with the quantity being the least of the questions.
Saying so is not a disclaimer bolted on at the end. It is the boundary that makes the rest of the page trustworthy: a calculator that is clear about what it does not answer can be believed about what it does.
Key Facts
- A cubic yard is 27 cubic feet, or 0.764555 cubic metres.
- A ten by ten foot slab at four inches is 33.3 cubic feet, 1.23 cubic yards, or 0.94 cubic metres.
- An eighty pound bag yields 0.60 cubic feet, confirmed on Quikrete Technical Data Sheet 1101-10 and the Sakrete Product Data Sheet, and derived as eighty pounds divided by a compacted density of 133 pounds per cubic foot, which is 0.6015.
- The same Quikrete data sheet lists a cured unit weight of approximately 140 pounds per cubic foot. Eighty divided by 140 is 0.5714 cubic feet, which is where the 0.56 to 0.58 figure in circulation comes from.
- Those are the same bag at two points in its life, plastic and cured, not a data sheet figure against a field one. A form holds plastic concrete, so 0.60 is the yield to order by.
- At 0.60 a cubic yard takes 45 bags. At 0.57 it takes 47.4, which is a cured volume comparison rather than an ordering figure.
- A sixty pound bag yields 0.45 cubic feet, a fifty pound bag 0.375, and a forty pound bag 0.30, giving 60, 72 and 90 bags per cubic yard.
- The yield per pound is constant across all four sizes at 7.5 cubic feet per thousand pounds, so a smaller bag is more bags to lift rather than better value.
- Both Quikrete and Sakrete conform to ASTM C387, the standard specification for packaged dry combined materials for concrete, with strength verified under ASTM C39 and density and yield under ASTM C138.
- Published guidance recommends a waste factor of five to ten percent, covering uneven subgrade, spillage during mixing, and over excavation. It applies to ready mix and to bags alike.
- The waste factor and the bag yield are different corrections. Only the waste factor survives a switch from bags to a truck.
- Published sources put the crossover between bags and ready mix at about one cubic yard, at one to one and a half, and at one and a half to two, and the spread is real because it turns on local figures.
- The decision turns on a short load fee published at around one hundred dollars, a minimum order published at one to three yards, the ordering increment, the site access, and the labour of mixing, published at two to three hours for one person to mix forty five bags.
- Water figures differ between published sources: one gives about 3.8 quarts per eighty pound bag, another advises starting with three quarts and adding as needed. Both agree that excess water is the commonest mistake, with published strength losses of up to forty percent and of thirty to fifty percent.
- Bagged mix has a published shelf life of six to twelve months stored dry and off the ground, and a bag that absorbs moisture begins to hydrate and develops hard lumps.
- A solid formed step flight is a stack of prisms: the top step is one rise deep and the bottom is n rises deep. Five steps four feet wide with a one foot run and a seven inch rise is 35.0 cubic feet as a stack and 29.2 as a wedge.
- Quikrete Concrete Mix is a 4000 psi average compressive strength blend for pours two inches thick or more.
Applications
- A homeowner pouring a shed base finds the bag count and the mixing time in the same place, and decides on the labour rather than the price.
- A contractor ordering ready mix sees the calculated need, the supplier increment and the minimum in sequence, and knows the order quantity before phoning.
- A DIY builder pouring steps learns that a formed flight is a stack of prisms rather than a wedge, and orders the twenty percent nobody told them about.
- Someone comparing bags against a truck sees the figures the decision turns on, and that a calculator does not know any of them.
- A reader who has seen the 0.57 yield quoted elsewhere finds out where it comes from and why it is not the figure to order by.
- A person about to mix their first bag reads the water figure and the strength consequence before they open it rather than after.
- An estimator checking somebody else's take-off finds the geometry mapping stated, and spots that a wall was computed with its height in the thickness term.
Worked Examples
Example 1. The reference slab, and why the volume is not the answer.
Given: a slab ten feet by ten feet at four inches thick.
Ten times ten times four twelfths is 33.3 cubic feet, which is 1.23 cubic yards or 0.94 cubic metres.
Result: correct, and not what to order. At ten percent waste the volume becomes 36.7 cubic feet, or 1.36 cubic yards. If it is going in as bags there is a second question after that, and if it is coming on a truck there is not.
Example 2. Where the two yields come from.
Given: an eighty pound bag of standard concrete mix.
The manufacturer data sheet gives 0.6 cubic feet, and the derivation is eighty pounds divided by a compacted density of 133 pounds per cubic foot, which is 0.6015. The same data sheet lists a cured unit weight of about 140 pounds per cubic foot, and eighty divided by 140 is 0.5714.
Result: two figures for one bag, and both are right. The first is the volume of plastic concrete that comes out of the bag and goes into the form. The second is what that concrete occupies once it has cured and consolidated.
A form holds plastic concrete, so 0.60 is the yield a bag count uses. The 0.57 that circulates elsewhere as a real world yield is not a mixing loss and not waste; it is the same material measured after it has set, and ordering by it would mean buying concrete to fill a volume the form never has.
Example 3. The bag count, and the comparison that is not one.
Given: the reference slab with ten percent waste, so 36.7 cubic feet, in eighty pound bags.
At the ordering yield of 0.60 that is 61.1 bags, rounded up to 62.
Result: 62 bags to buy. Where the cured yield is displayed alongside, the same volume at 0.57 is 64.3 bags, and that figure appears as an explanation of the lower yield in circulation rather than as an alternative order. Per cubic yard the same comparison is 45 bags against 47.4.
No path on this page produces an order at the cured yield, because a form does not hold cured concrete.
Example 4. The two corrections have different sizes.
Given: the reference slab, in eighty pound bags at the ordering yield.
The theoretical volume is 33.3 cubic feet, which is 55.6 bags. The ten percent waste factor adds 5.6 bags, taking it to 61.1.
Result: the waste factor is worth 5.6 bags here. The gap between the two yields, if the cured figure were used, would be 3.2 bags. Different sizes, different causes, and only the first one survives if the concrete arrives on a truck instead.
Example 5. A wall is not a slab.
Given: a wall twenty feet long, eight feet high and eight inches thick.
A wall uses the length, the height in place of the width, and the thickness. Twenty times eight times eight twelfths is 106.7 cubic feet, or 3.95 cubic yards.
Result: 106.7 cubic feet. An engine that takes the height as a thickness and the thickness as a width computes a different object entirely, and the number it returns looks perfectly reasonable, which is why the mapping is stated on every result.
Example 6. A formed stair is a stack, not a wedge.
Given: a solid formed step flight, five steps, four feet wide, one foot run, seven inch rise.
A solid flight is a stack of prisms. The top step is one rise deep, the bottom is five rises deep, so the flight is five times six over two, which is fifteen rises deep in total.
Four times one times seven twelfths times fifteen is 35.0 cubic feet.
Result: 35.0 cubic feet, or 1.30 cubic yards. The same envelope treated as a triangular wedge is 29.2 cubic feet, about twenty percent less, and that is what an unformed earth slope would be rather than formed concrete steps.
Open risers, a landing, or steps poured over fill are different volumes again, and the page asks which kind of flight it is before it computes anything rather than assuming.
Example 7. The round pour that is four times out.
Given: a post hole twelve inches across and three feet deep.
The diameter is one foot, so the radius is half a foot. Pi times a half squared times three is 2.36 cubic feet.
Result: 2.36 cubic feet. Enter the same twelve inches as a radius and the answer becomes 9.42, four times larger. The error runs the other way just as easily, and on a pour that has to be finished in one go a factor of four is not a rounding difference.
The depth here is three feet. Depths, thicknesses and rises are converted to feet at entry rather than inside the equations, so a three cannot be read as three inches in one place and three feet in another.
Example 8. Ordering a truck, in four steps.
Given: the reference slab at ten percent waste, so 1.36 cubic yards, from a supplier with a quarter yard increment and a two yard minimum.
The calculated need is 1.36 cubic yards. Rounded up to the quarter yard increment it is 1.50. Against a two yard minimum the order is 2.00.
Result: order 2.00 cubic yards for a job that needs 1.36. The supplier minimum governs what is delivered rather than what is needed, and the four figures are reported in sequence so the reader can see where each step took them.
No bag yield question arises. The waste factor still does, because the hole is still bigger than the drawing.
Example 9. What forty five bags actually is.
Given: a cubic yard, in eighty pound bags.
At the ordering yield that is 45 bags. Published guidance puts mixing that at two to three hours for one person.
Result: 45 bags and an afternoon. That figure appears on neither the bag price nor the ready mix quote, and it decides the answer for most people choosing between them. The crossover published across sources runs from about one cubic yard to about two, and it moves with the short load fee, the minimum order, the increment and the site access, none of which a calculator knows unless it is told.
Example 10. The one number that costs strength.
Given: an eighty pound bag about to be mixed.
Published sources give the water requirement as about 3.8 quarts, and another advises starting with three quarts and adding as needed.
Result: use the figure on the bag. Both sources agree on what matters, which is that excess water is the commonest mistake with bagged concrete, with published strength losses of up to forty percent and of thirty to fifty percent.
The requirement is product specific and this page does not scale the eighty pound figure to the smaller bags. Everything else here costs money when it is wrong. This one weakens the concrete, and it looks better while it does it: more water makes the mix easier to place and the result indistinguishable until it is loaded.
Standards & References
- ASTM C387 Standard Specification for Packaged, Dry, Combined Materials for Mortar and Concrete The standard both Quikrete and Sakrete state conformance to for bagged concrete mix, covering the packaged product rather than the design of what is poured with it.
- ASTM C138 Standard Test Method for Density, Relative Density and Air Content of Concrete The test method behind the density figures used to derive a bag yield, and the reason a yield is a density calculation rather than a measured volume.
- ASTM C39 Standard Test Method for Compressive Strength of Cylindrical Concrete Specimens The strength test referenced by the bagged product data sheets.
- Quikrete Concrete Mix product page and technical data The 4000 psi average compressive strength blend for pours two inches thick or more, the eighty pound bag under model number 110180, and the data sheet numbered 1101 that carries both the compacted density used for the yield and the cured unit weight.
- Sakrete Concrete Mix product page and data sheet The comparable product stating conformance to ASTM C387 and listing the same 0.6 cubic feet yield for an eighty pound bag.
- Portland Cement Association, Concrete Technology and mixing guidance Background on water to cement ratio and why excess mixing water reduces strength, which is the mechanism behind the published warnings on bagged product.
Units
Volume is entered and reported in cubic feet, cubic yards and cubic metres. A cubic yard is 27 cubic feet and 0.764555 cubic metres, and a cubic foot is 0.0283168 cubic metres. The reference slab is 33.3 cubic feet, 1.23 cubic yards and 0.94 cubic metres.
Lengths, widths, heights, diameters and step runs are entered in feet, with metres alongside at 0.3048. Ten feet is 3.048 metres.
Thicknesses, depths and step rises are entered in inches, with millimetres alongside at 25.4. Four inches is 102 mm and seven inches is 178 mm.
Those two groups are converted to a single canonical unit, feet, before any volume equation runs. That is a deliberate choice rather than a detail: a depth of three means three feet in one convention and three inches in another, and converting at entry removes the ambiguity from every equation downstream.
Bag weights stay in pounds in the US sizes, with the kilogram equivalent alongside at 0.453592. An eighty pound bag is 36.3 kg. Metric markets sell 20 kg, 25 kg and 40 kg bags, which are a different product list rather than a conversion of the US sizes, so their yields are entered rather than derived from the pound figures.
Bag yield is in cubic feet with litres alongside. An eighty pound bag at 0.60 cubic feet is 17 litres. Density is in pounds per cubic foot with kilograms per cubic metre alongside at 16.0185: the compacted figure of 133 pounds per cubic foot is 2131 kg per cubic metre, and the cured figure of 140 is 2243.
Water is in quarts and litres at 0.946353. Three point eight quarts is 3.60 litres.
The internal unit selector governs the fields, labels, math, on-screen result and any exported result, and it takes priority over any site-wide unit switch. Switching converts the values you entered rather than reinterpreting them.
Limitations
- This page returns a quantity and issues no verdict. There is no code table and no minimum for a volume of concrete, so nothing here passes or fails.
- It does not design a mix. Strength class, proportioning, admixtures and the water to cement ratio are mix design and are outside it.
- It does not design a structure. Whether a slab is thick enough, what reinforcement it needs, and whether the thing being poured should be poured at all are separate questions. Permitted structural work, foundations, retaining walls and commercial projects may require design by a licensed professional, and this calculator computes quantity only.
- It models a solid formed step flight as a stack of prisms. Open risers, a landing, and steps poured over fill are different volumes and the page stops rather than approximating them.
- It never orders at the cured yield. That figure is shown to explain the lower number in circulation, and it is not applied to the sixty, fifty or forty pound bags at all because their cured unit weights have not been confirmed.
- It does not know your supplier. The short load fee, the minimum order, the ordering increment and the delivery access all decide the answer and none of them is knowable from dimensions.
- It does not scale the water figure between bag sizes. The requirement is product specific and the figure on the bag governs.
- It does not estimate cost beyond arithmetic on a price you enter. With no price entered, no cost is reported rather than a default being assumed.
- It does not cover formwork, subgrade preparation, compaction, curing, finishing, joint layout, or hot and cold weather placement.
- The waste factor is a stated allowance rather than a measurement of your excavation. A site with a poor subgrade can exceed ten percent and this page has no way to know it.
- Where a dimension is unusual for the selected pour type the page says so and asks you to confirm it was intended. That is a prompt to check the entry, not a judgement on whether the thing being poured is adequate.
Common Mistakes to Avoid
- Ordering the theoretical volume. It is correct arithmetic and it is not what fills the form.
- Combining the waste factor and the bag yield into one percentage. They have different causes and different sizes, and only the waste factor applies if the concrete arrives on a truck.
- Ordering by the cured yield. The 0.57 cubic feet figure is the same bag after it has consolidated, not a mixing loss. A form holds plastic concrete and 0.60 is the yield to buy by.
- Applying the cured yield to a smaller bag. The relationship is a density ratio and the cured unit weights for the sixty, fifty and forty pound products have not been confirmed.
- Entering a radius in the diameter field. A round pour taken from a radius is four times too large, and from a diameter read as a radius four times too small.
- Mixing the units on a depth. A three is three feet in one convention and three inches in another, which is why this page converts at entry and states which unit each field takes.
- Computing a wall as a slab. A wall uses its height in the width term. Mixing the terms produces a plausible number for a different object.
- Treating a formed stair as a wedge. A solid flight is a stack of prisms and it is about twenty percent more concrete than the sloped envelope containing it.
- Calculating steps without saying what kind they are. Open risers, a landing and steps over fill are all different volumes from a solid formed flight.
- Assuming a supplier delivers what you calculated. Orders go in increments above a minimum, and the minimum governs what arrives.
- Ignoring the mixing labour. Forty five eighty pound bags is a cubic yard and a published two to three hours, and it appears on neither price.
- Buying a smaller bag for value. The yield per pound is constant at 7.5 cubic feet per thousand pounds across all four sizes, so a smaller bag is only more bags.
- Adding water to make mixing easier. Published sources put the strength loss from excess water at up to forty percent and at thirty to fifty percent, and the mix looks better while it happens.
- Mixing every bag you bought. The rounded count is a purchase, not an instruction. Water goes in per bag according to the bag.
- Storing bags on the ground. Published shelf life is six to twelve months dry and off the ground, and a bag that takes up moisture begins to hydrate and lumps.
- Quoting a crossover between bags and ready mix as a fixed volume. Published sources put it anywhere from one to two cubic yards and the spread is real.
Frequently Asked Questions
How many bags of concrete are in a cubic yard?
How much concrete does an eighty pound bag make?
Why do some sources say 0.57 cubic feet instead?
How much waste factor should I add?
How much concrete do I need for a ten by ten slab?
Is it cheaper to use bags or order ready mix?
How do I calculate concrete for steps?
How much water goes in a bag of concrete?
Frequently Used Together
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Calculate
This selector governs every field, label, result and export here and takes priority over the site header switch. Switching converts what you entered rather than reinterpreting it, so 10 ft becomes 3.048 m and returns to exactly 10.
The Pour
Choose this first. It decides which dimensions are asked for and which term each one feeds, because a slab, a footing and a wall run through the same equation with different measurements in different places.
Leave empty for one. Four identical footings is four times the volume, and this is the only place on this page where a quantity multiplier is the right move.
How It Is Supplied
It decides whether the bag yield question applies at all. Not decided is an answer: it returns both routes side by side with the bag count at all four US sizes.
It covers an uneven subgrade, spillage during mixing and over excavation, and it applies to a truck delivery exactly as it applies to bags. None is a valid answer rather than a blank one.