Gravel Calculator — A Cubic Yard on the Truck Is Not a Cubic Yard on the Ground

Loose Versus Compacted Cubic Yards

Aggregate volume has three states and one name, and almost every ordering mistake starts there.

Bank cubic yards are material undisturbed in the ground, before anything is dug.

Loose cubic yards are material excavated and in the truck. Breaking up the interlocked structure fills the spaces between particles with air, so the same mass takes up more room.

Compacted cubic yards are material placed, spread and rolled. Air is driven out and the particles are forced together, so the same mass takes up the least room of the three.

Published guidance states it plainly: always clarify whether a quantity is expressed in bank, loose or compacted cubic yards.

The reason it matters on a gravel order is that two documents use the same word for different states and neither says so.

A drawing, a specification or a finished depth is a compacted quantity. It describes what is on the ground after the roller has been over it.

A supplier quote and a delivery ticket are loose quantities. They describe what is in the truck.

Nobody is being careless. Within its own trade neither document needs to say which state it means, because everyone in that trade already knows. The reader standing between the two is the one who has to translate.

On this page the finished volume is compacted and the order volume is loose, and both are labelled on the result. Reading a loose figure as a compacted one, or the reverse, is not a rounding difference: on crushed stone base it is a sixth to a quarter of the whole order.

A third factor sits in the same family and is easy to confuse with compaction. Swell is the bank to loose conversion, not the loose to compacted one. Published figures give crushed stone a swell of 10 to 15 percent, sand and gravel 10 to 12 percent, and clay 30 to 40. This page starts from a finished depth rather than from an excavation, so swell does not arise here, and it is named because a reader who meets the word will otherwise apply it to the wrong pair of states.

One caution from the same source: the relationship between the three states is not always linear, so a volume cannot always be moved between them by multiplying once.

Gravel Compaction Factor

The compaction factor converts the volume you want on the ground into the volume that has to arrive on the truck, and it is not one number.

Published estimating guidance gives it for crushed stone base material compacted to 95 percent Modified Proctor density: the compacted volume is typically 80 to 85 percent of the loose volume, so 1.15 to 1.25 loose cubic yards are needed for every compacted cubic yard in place.

Two things about that sentence do most of the work.

It is a range, and the range is not vagueness. It reflects real variation in gradation, moisture and the effort applied.

And it is tied to a specification. Ninety five percent Modified Proctor is a stated compaction target, tested under ASTM D1557, with ASTM D698 covering the Standard Proctor test. The factor moves with what the material is compacted to, so a factor quoted without its specification is incomplete.

Two calculator sites give 1.25 and 1.20 for dense graded base and present them as settled figures. They are two points inside the published range, and neither states the specification the range depends on.

The factor is also a property of the material rather than of the job, which is the part most calculators get wrong.

Crusher run and other dense graded bases are graded from fines up to about three quarters of an inch. Under a roller the small particles migrate into the voids between the large ones and the whole mass loses volume. That is what a compaction factor describes.

Clean open graded stone such as number 57 has no fines to migrate. Rounded pea gravel has no fines and no angular faces to lock together. One published source states that neither compacts and that they get no allowance at all. Another gives clean stone 1.10.

That one is not settled. The estimating source with the specification behind it addresses base material rather than clean stone, so this page reports both figures for clean and rounded materials and issues no single order volume for them.

Where a supplier gives a factor for the specific material, that figure wins and the page uses it alone. The pit knows how its own stone behaves under a roller and no published table does.

What the page never does is average. The midpoint of 1.00 and 1.10 is 1.05, which appears in no source, and a reader who quoted it to a supplier would be using a number that exists nowhere.

Gravel Waste Allowance

Waste is the second correction and it covers the site rather than the stone.

Published guidance recommends adding five to ten percent to the calculated quantity for most jobs, and closer to fifteen percent on areas with no hard borders to hold the material in place.

What it pays for is an uneven subgrade that is deeper in places than the drawing says, spillage while spreading, edges that are not square, and material that ends up outside the area. One source puts the reason plainly: ordering slightly long is cheaper than paying for a second delivery.

Published guidance also states that waste and compaction are two separate things, each added once. The field routinely merges them into a single percentage.

They multiply rather than add. A compaction factor of 1.25 with a ten percent waste allowance is a combined multiplier of 1.375. Adding twenty five and ten gives 1.35, which is 1.8 percent below the correct 1.375.

The arithmetic error is small. The consequence of merging is not, and it has nothing to do with the 1.8 percent.

A combined figure cannot be taken apart. The two corrections answer to different things: waste to the ground and the crew, compaction to the stone. Change the material and one of them moves while the other does not, and on clean open graded stone the compaction allowance may go to nothing while the waste allowance stays at ten percent.

A reader working from a single thirty five percent has no way to make that adjustment, and no way to see that one of the two even applies to their material.

So this page applies them at separate stages, reports the volume each one produced, and shows the combined multiplier alongside rather than instead.

Gravel Tons Per Cubic Yard

Suppliers price by the ton even when a reader specifies yards, so somewhere between the drawing and the invoice a volume is converted using a density. That conversion is where the money is.

Published figures in tons per cubic yard run from about 1.2 for river rock, through 1.3 to 1.35 for pea gravel, 1.4 for crushed stone and number 57, 1.5 for dense graded base and crusher run, to about 1.85 for riprap.

River rock to riprap is a factor of about 1.54 on the same cubic yard. Two materials filling the same hole differ by half as much again on a ticket priced by weight.

Published criticism names the failure directly: a generic 2,410 pounds per cubic yard, used by many calculators, understates dense crusher run, which is 2,700 or more. That is not a small approximation. It is out by a fifth on the densest common material.

Two things make a published density weaker than it looks.

Most figures do not say which volume state they describe. An estimating source gives aggregate base course at 115 to 130 pounds per cubic foot, which is 1.55 to 1.75 tons per cubic yard, and names it as the compacted density. The calculator figures give no state at all, which is the same fault in the weight that the three states problem is in the volume.

And moisture moves it. One source puts damp or compacted material fifteen to twenty five percent above dry loose stone. A load delivered after rain weighs more than the same volume delivered in August.

Where a source gives a range this page reports a range, because choosing a point inside a published range is a decision it has no basis to make. Where a supplier gives a density for the material coming out of their pit, that figure wins and produces a single tonnage.

The practical advice is short. Ask the supplier what their material weighs per yard. They know, it is on their scale ticket, and it beats every published table including the ones on this page.

Gravel Delivery Minimum

Bulk aggregate is delivered by the truck load, and published guidance puts the minimum at five to ten tons.

That figure decides more small jobs than the arithmetic does.

A path of a hundred square feet at three inches is about 0.93 cubic yards, or roughly 1.3 tons. Every minimum quoted is at least four times that.

So the order is the minimum. The calculated quantity has no bearing on what arrives or what is paid for, and a calculator that returns 1.3 tons and stops has answered a question the reader cannot act on.

What changes at that point is the question itself. It stops being how many yards and becomes whether to buy bagged material, whether to collect a load rather than have one delivered, and whether the delivery charge on a minimum load makes bags cheaper despite a much higher unit price.

This page reports the minimum where a reader enters one, names the published five to ten ton range where they do not, and says when an order falls below it. It does not compute a bag count, because bag weights and yields are not held here and a count without them would be invented.

The minimum varies by supplier and by region, and it is worth one phone call before any of the arithmetic on this page matters.

Driveway Gravel Depth

A gravel driveway is not one depth of one material, and treating it as one is the commonest way the quantity comes out short.

Published guidance gives four to six inches compacted under driveways, slabs and pavers, placed in two to four inch lifts because a thicker lift does not compact through.

For a full new gravel driveway the published figure is eight to twelve inches total, in two or three layers.

Those layers are not the same material. A driveway is described as a base of angular dense graded stone with a top layer of one to two inches of angular surface stone, and on soft soil or under heavy traffic the base goes to six inches or more.

So a full driveway is two or three calculations, each at its own depth and often in its own material, with its own compaction factor and its own density. This page calculates the layer you entered. It says so on every driveway result, because a reader who enters twelve inches of one material has priced something that is not what published guidance describes.

The material matters as much as the depth here. Published guidance is consistent that crusher run locks together and holds under wheels, and that rounded pea gravel shifts under tyres. One source puts it as rounded stone never stopping rolling.

That is guidance and not code. This page reports it and computes whatever material was chosen, because refusing would be inventing a prohibition and computing silently would be withholding something every source agrees on.

And the depths themselves are published ranges rather than design figures. A vehicle area carries loads that depend on the subgrade, the drainage and the traffic, and none of those is knowable from an area and a depth.

Drainage Gravel Versus Compacted Base

Drainage stone and base stone are chosen for opposite reasons, and the property that makes one work is the property that disqualifies the other.

A compacted base needs fines. Dense graded material runs from dust up to about three quarters of an inch, and under a roller the small particles migrate into the voids between the large ones. The mass locks together, loses volume and becomes a hard surface that carries load.

A drain needs the voids to stay open. Published guidance calls for washed clean stone with no fines, so water can move through the spaces between the particles. Number 57 is the common size for it.

Fines in a drain do the same thing they do in a base: fill the voids. In a base that is the point. In a drain it is the failure.

Two consequences follow for this calculation.

Clean stone does not compact in the way a base does, because there is nothing to migrate. That is why the compaction factor on this page depends on the material, and why one published source gives clean open graded stone no allowance at all.

And a drainage depth is not a surface depth. The published ranges on this page cover paths, driveways and paver bases, which are surfaces carrying something. A drain is sized by how much water has to move and where it goes, so this page reports no depth range for a drainage application and says why.

What this page does is name the requirement and compute the quantity. Trench width, pipe, geotextile, outfall and the drainage design itself are outside it.

What Is a Gravel Calculation

A gravel calculation turns an area and a depth into a quantity to buy, and the difficulty is that the quantity has three forms and two of them are hidden.

The volume itself is not in dispute. Area multiplied by depth, divided into cubic yards, is arithmetic every calculator gets right.

What follows is where the trade's own vocabulary works against a reader. The same stone is measured in the ground, in the truck and on the ground, and the three are different numbers with one name.

The second hidden form is weight. Suppliers price by the ton, so a density stands between the volume and the invoice, and it varies by a factor of one and a half across ordinary materials.

So the useful output of a gravel calculation is not a volume. It is an order: a loose volume, converted at a density that belongs to the specific stone, with the waste the site needs, checked against the minimum the supplier will deliver.