Electrical Load Calculator — NEC 220 Residential Service Sizing

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Method & Code

Standard method (Part III) applies separate demand factors per load category. Optional method (220.82) groups loads and often gives a lower result when the dwelling is eligible.

NEC 2023 references are used for all calculations. NEC 2026 restructures the load-calculation provisions — verification against its text is pending.

Dwelling

Habitable area only — exclude open porches, garages, and unfinished spaces not adaptable for future use. ft²: 3 VA/ft² (Table 220.12); m²: 33 VA/m² (code value, not a unit conversion).

Minimum two required per 220.52(A), at 1,500 VA each. Default: 2.

At least one required per 220.52(B), at 1,500 VA each. Default: 1.

Appliances

One household range, nameplate kW. ≤ 12 kW → 8,000 VA demand. Above 12 kW Table 220.55 Note 1 adds 5% per kW. Maximum 27 kW.

One household dryer, nameplate kW. Demand = max(5,000 VA, nameplate) per 220.54.

Sum of nameplate VA for all fixed appliances (water heater, dishwasher, disposal, etc.) — not the range or dryer. Standard method applies 75% demand when count ≥ 4.

Count drives the 75% factor in the standard method when count ≥ 4. Leave blank to assume fewer than 4 (100% demand). Not used in optional method.

HVAC

Nameplate VA of all air-conditioning equipment. Only the larger of AC and heat enters the total (220.60 / 220.82(C)).

Nameplate VA of all electric heating equipment. Only the larger of AC and heat enters the total. In the optional method, enter the heating type below.

Other Loads

Nameplate VA of the largest single motor. Standard method adds 25% of this value (220.50). Optional method includes it in general loads at nameplate.

EVSE nameplate VA. Taken at ×1.25 as a continuous load per 625.42. Load-management systems are not modeled.

Service

120/240 V single-phase is the standard for one-family dwellings. Default: 240 V. Three-phase is out of scope for this version.

Enter your existing or planned service ampere rating to get an adequacy verdict. Leave blank to see only the calculated load and recommended size.

Overview

Use this tool to work out how much electrical load a house actually places on its service and what size that service has to be. Enter the floor area, the kitchen and laundry circuits, the major appliances, and the heating and cooling loads; the NEC Article 220 demand factors are applied and the result is the calculated load in volt-amperes and amperes, with the minimum standard service size.

Two code-recognized methods are available. The standard method (Article 220, Part III) applies separate demand factors to lighting, ranges, dryers, and fixed appliances. The optional method (220.82) groups the general loads and applies a single 100-percent-then-40-percent factor; when the dwelling is eligible for it, it often produces a smaller figure for the same house. The breakdown is shown line by line with the code reference for each step.

If you enter your existing service rating, the result screens it against the sizing basis — the larger of the calculated load and the 100 A minimum that the code sets for a one-family dwelling — and reports adequate or undersized with the margin. The output is the load calculation itself; conductor, breaker, and panel design are separate steps. References follow the 2023 edition; the 2026 NEC restructures the load-calculation provisions, so verify edition-specific section numbers before using the result for a submittal.

What to Look at First

When you click Calculate, look at these outputs in order:

  • The calculated load in VA and amperes, and the recommended standard service size
  • Whether the screen ran against the calculated amps or the 100 A code minimum — when 100 A governs, the sizing basis is 100 A regardless of the load
  • The verdict against your existing service, if you entered one, with margin or shortfall
  • The line-by-line breakdown showing what each load contributed after its demand factor
  • Which method produced the figure — standard or optional — since the two can differ by 20–30 A on the same house
  • Which NEC edition the references follow
  • Which defaults were applied (two small-appliance circuits, one laundry circuit, 240 V)

If the result is INFEASIBLE, floor area is missing or — in the optional method — a heat load was entered without selecting the heating type. If the result is INVALID-INPUT, one or more values are outside valid ranges.

How to Use This Calculator

  1. Pick the calculation method. The standard method follows NEC Article 220, Part III, with separate demand factors per load category. The optional method follows 220.82 and often yields a smaller load — it applies to dwellings with a 100 A or larger service, so verify eligibility before sizing from its result.

  2. Enter the floor area in square feet or square meters. Count habitable space only — open porches, garages, and unfinished spaces not adaptable for future use stay out of the figure.

  3. Keep or adjust the circuit counts. The code requires at least two small-appliance circuits and one laundry circuit, at 1,500 VA each; the defaults are exactly that.

  4. Add the appliances: one household range and one dryer by nameplate kilowatts, the other fixed appliances (water heater, dishwasher, disposal) as a total VA with their count, the air-conditioning and electric-heat loads, the largest motor, and an EV charger if there is one. In the optional method, entering electric heat also requires the heating type, because the 220.82(C) factor depends on it.

  5. Enter your existing or planned service rating in amps if you want the adequacy screen; leave it blank to get just the load and the recommended service size.

  6. Read the result. The headline is the load in VA and amps with the recommended service; the breakdown shows each demand step with its NEC code section.

All inputs are empty by default. Fill in the values that apply to your dwelling and leave the rest blank.

Inputs & Outputs

Inputs

  • •Calculation Method — Options: Standard Method — Article 220, Part III, Optional Method — 220.82
  • •NEC Edition — Options: NEC 2020, NEC 2023 (default), NEC 2026 (pending verification)
  • •Floor Area
  • •Small-Appliance Circuits (circuits)
  • •Laundry Circuits (circuits)
  • •Range Nameplate (kW)
  • •Dryer Nameplate (kW)
  • •Fixed Appliances — Total VA (VA)
  • •Fixed Appliances — Count (appliances)
  • •Air-Conditioning Load (VA)
  • •Electric Heat Load (VA)
  • •Heating Type (220.82(C)) — Options: Central or fewer than 4 units (×65%), Four or more units (×40%), Heat pump (×100%)
  • •Largest Motor (VA)
  • •EV Charger Nameplate (VA)
  • •Service Voltage (V)
  • •Existing Service Rating (A)

Outputs

  • •Total Calculated Load (VA)
  • •Service Current (A)
  • •Sizing Basis (A)
  • •Recommended Service Size (A)
  • •Service Margin (%)
  • •Service Shortfall (A)
  • •Service Status

Formula

General Loads (both methods)

lighting_VA = area_ft² × 3           (Table 220.12)
           = area_m²  × 33          (code value for metric — not a unit conversion)
general_VA  = lighting_VA + small_appliance_circuits × 1,500 + laundry_circuits × 1,500

Standard Method (Part III)

lighting demand = first 3,000 VA @ 100% + next portion to 120,000 @ 35% + remainder @ 25%  (Table 220.42)
range:  ≤ 12 kW → 8,000 VA;  12–27 kW → 8,000 × (1 + 0.05 per kW above 12)               (Table 220.55, Note 1)
dryer:  max(5,000 VA, nameplate × 1,000)                                                   (220.54)
fixed appliances: × 0.75 when count ≥ 4, else × 1.00                                      (220.53)
HVAC: larger of AC and heat                                                                (220.60)
largest motor: + 25% of nameplate VA                                                       (220.50)
EV charger: × 1.25                                                                         (625.42)
total_VA = sum of all demand lines

Optional Method (220.82)

general_total  = general_VA + range nameplate + dryer nameplate + fixed VA + motor VA
general demand = first 10,000 VA @ 100% + remainder @ 40%                                 (220.82(B))
heating factor = 65% central or < 4 units | 40% four or more units | 100% heat pump       (220.82(C))
HVAC demand    = larger of (AC × 100%) and (heat × factor)
EV charger     = × 1.25
total_VA = general demand + HVAC demand + EV

Service Sizing

amps             = total_VA ÷ voltage              (single-phase 120/240 V)
sizing basis     = max(amps, 100)                  (230.79(C): 100 A minimum, one-family dwelling)
recommended size = smallest standard rating ≥ basis (100, 110, 125, 150, 175, 200, 225, 250, 300, 350, 400, 450, 500, 600 A)

Decision Screen

status = INFEASIBLE         if floor area is missing, or optional method + heat_va > 0 and no heating type
       = INVALID-INPUT      if any input is outside valid range
       = COMPUTED           if no existing service was entered
       = SERVICE-ADEQUATE   if existing ≥ sizing basis
       = SERVICE-UNDERSIZED if existing < sizing basis

margin = (existing − sizing basis) / sizing basis
margin bands:
  MINIMAL  — 0% ≤ margin < 15%
  MODERATE — 15% ≤ margin < 50%
  AMPLE    — margin ≥ 50%

The screen runs against the sizing basis, not raw amps. A 90 A service on an 80 A load fails because the sizing basis is max(80, 100) = 100 A (the 230.79(C) floor), not because the load exceeds 90 A.

Standard Method vs Optional Method

The standard method (Article 220, Part III) applies separate demand factors to each load category: a tiered lighting demand that drops to 35 percent above 3 kVA, an 8 kVA demand for a range up to 12 kW, a 5 kVA dryer floor, and a 75 percent factor for fixed appliances when there are four or more. Each load is treated individually, and the total is the sum of those individual demands.

The optional method (220.82) groups all general loads — lighting, circuits, range, dryer, fixed appliances, and motor — and applies a single two-tier factor: 100 percent on the first 10 kVA and 40 percent on everything above it. HVAC is handled separately with 220.82(C) heating factors. Because the 40 percent second tier suppresses a larger share of the load, the optional method often produces a smaller total when the dwelling has substantial above-threshold general load.

The tradeoff is eligibility: the optional method is only code-recognized for dwellings that meet the 220.82 conditions, including an existing or planned service of 100 A or larger. Use the standard method when eligibility is in doubt, or when a permit reviewer requires the more conservative figure. Use the optional method — and verify eligibility — when the result will drive an upgrade decision where every ampere matters.

The 100 A Minimum

Section 230.79(C) sets a 100 A minimum service for any one-family dwelling, regardless of the calculated load. The adequacy screen runs against the sizing basis — the larger of the calculated amperes and 100 A — not against the raw calculated load alone.

This matters whenever the calculated load falls below 100 A. A small, lightly loaded house on gas heat might calculate to 60 or 70 A. That result is arithmetically valid, but the 100 A floor governs the service size and the adequacy verdict. A 90 A service fails not because the house needs 90 A, but because the code minimum for a one-family dwelling is 100 A and 90 A does not meet it.

The 100 A floor is why Example 3 below results in SERVICE-UNDERSIZED even though the calculated load is only 80 A: the sizing basis is max(80, 100) = 100 A, and the existing 90 A service is below it.

What is a Residential Load Calculation

A residential load calculation is the NEC-required process for determining the minimum service size for a one-family dwelling. It applies code-specified demand factors to the dwelling's loads, sums them, and divides by the service voltage to get amperes. The result is the code's sizing floor — not a prediction of actual peak demand, but a conservative basis for service design.

The key difference between a load calculation and a circuit-by-circuit nameplate sum is demand diversity: not all loads run simultaneously at full nameplate. The NEC demand factors encode that diversity statistically. The lighting demand, for example, reduces everything above 3 kVA to 35 percent on the assumption that not every light runs at full load simultaneously.

The result drives three decisions: what service size to install for a new house, whether an existing service can accept a new load, and whether a permit reviewer's load calculation requirement is met. The calculation is required whenever a permit is pulled for service work, and it is the basis the inspector and engineer of record use to verify the design.

Key Facts

  • General lighting load is 3 VA per ft² of habitable area; the code's metric value is 33 VA per m².
  • Every dwelling needs at least two small-appliance circuits and one laundry circuit, at 1,500 VA each, before any demand factor.
  • The standard lighting demand takes the first 3,000 VA at 100 percent and the portion up to 120,000 VA at 35 percent.
  • One household range up to 12 kW counts as 8,000 VA; above 12 kW it grows 5 percent per kilowatt.
  • A dryer counts as its nameplate or 5,000 VA, whichever is larger.
  • Heating and cooling are non-coincident: only the larger of the two enters the total.
  • The optional method takes the first 10 kVA of general loads at 100 percent and the remainder at 40 percent, and often supports a smaller service when the dwelling is eligible.
  • A one-family dwelling service is never smaller than 100 A, whatever the calculated load.
  • EVSE enters at 125 percent as a conservative continuous-load screen; managed EV load is flagged but not modeled.

Applications

  • Sizing the service for a new house or a major remodel before the panel is ordered
  • Checking whether an existing 100, 150, or 200 A service can absorb an EV charger or electrified heat
  • Comparing EV charger sizes against the headroom of an older service
  • Comparing the standard and optional methods when an upgrade decision is borderline
  • Preparing the load calculation sheet a plan reviewer or AHJ asks for with a permit
  • Screening an accessory dwelling unit or addition against the existing service
  • Estimating whether a panel upgrade is needed before a heat-pump conversion
  • Exam preparation on Article 220 dwelling calculations, with the breakdown shown per code section

Example Calculation

Example 1 — Standard method, 2,000 ft² all-electric house Two small-appliance circuits, one laundry circuit, a 12 kW range, a 5 kW dryer, a 4,500 VA water heater, 5 kW of air-conditioning against 10 kW of electric heat, 240 V.

General: 2,000 × 3 + 2×1,500 + 1,500 = 10,500 VA Lighting demand: 3,000 + 0.35 × 7,500 = 5,625 VA (Table 220.42) Range: 8,000 VA (Column C) Dryer: 5,000 VA Appliances: 4,500 VA HVAC: max(5,000, 10,000) = 10,000 VA (220.60) Total: 33,125 VA → 33,125 ÷ 240 = 138.0 A → 150 A service

Example 2 — Optional method, same house General total: 10,500 + 12,000 + 5,000 + 4,500 = 32,000 VA Demand: 10,000 + 0.40 × 22,000 = 18,800 VA (220.82(B)) HVAC: max(5,000 × 1.00, 10,000 × 0.65) = 6,500 VA (220.82(C)) Total: 25,300 VA → 105.4 A → 110 A service The same house, 28 A apart between methods — the optional method often sizes lower when the dwelling is eligible.

Example 3 — The 100 A floor governs A small gas-heated house calculates to 19,200 VA, or 80.0 A. The owner's existing service is 90 A. Sizing basis: max(80.0, 100) = 100 A Screen: 90 A < 100 A → SERVICE-UNDERSIZED The load itself fits, but a one-family dwelling service may not be smaller than 100 A, so the 90 A service fails on the code minimum, not on the load.

Example 4 — Adding an EV charger The Example 1 house adds a 9.6 kW EV charger. EV demand: 9,600 × 1.25 = 12,000 VA (continuous load) Total: 33,125 + 12,000 = 45,125 VA → 188.0 A → 200 A service An approved and documented load-management system can change the EV load that enters the calculation; that path is flagged but not modeled here.

Standards & References

Key sections used: Table 220.12, 220.52, Table 220.42, Table 220.55 with Note 1, 220.54, 220.53, 220.60, 220.50, 220.82, 230.79(C), 240.6. The 2026 edition of the NEC restructures the load-calculation articles; this page follows the NEC 2023 Article 220 references, and 2026 section numbers should not be used until the edition profile is verified. Local amendments and the authority having jurisdiction govern.

Units

Floor area is entered in square feet or square meters. The general lighting density is 3 VA per ft²; for metric entry the code's own value of 33 VA per m² is used rather than a unit conversion — the two differ by about two percent, and the code figure governs. Loads are in volt-amperes, with the range and dryer entered in nameplate kilowatts. The calculated load is shown in VA and amperes at the service voltage, 240 V single-phase by default. Service sizes follow the standard ampere ratings from 100 to 600 A. There is no length or mass to convert in this calculator; units switch only between ft² and m², applying the respective code values.

Limitations

  • Covers a single dwelling unit on a 120/240 V single-phase service; three-phase and 208Y/120 V services are out of scope.
  • Supports one household range and one dryer; multiple cooking appliances and multi-dryer demand tables are not modeled.
  • Produces the load calculation only — neutral sizing, conductor and breaker selection, and panel layout are separate steps.
  • Multifamily services (220.84) and the metered-demand method for existing dwellings (220.87) are not covered.
  • The optional method result applies only where the dwelling meets the 220.82 eligibility conditions; verify before sizing from it.
  • EVSE enters at 125 percent; load-management and power-control systems are not modeled beyond a note on the EV line.
  • The NEC 2026 edition restructures these provisions; references follow the 2023 edition until the 2026 text is verified.
  • Demand values are code values, but local amendments and the AHJ's interpretation govern the accepted result.

Common Mistakes to Avoid

  • Counting the garage, open porch, or unfinished basement in the floor area. The 3 VA figure applies to habitable space.
  • Skipping the small-appliance and laundry circuits. They add 4,500 VA before any appliance is entered, and two kitchen circuits are the code minimum.
  • Adding both heating and air-conditioning. They are non-coincident; only the larger one counts.
  • Entering the range at nameplate in the standard method. A 12 kW range counts as 8,000 VA under Table 220.55.
  • Forgetting the 5,000 VA dryer floor when the nameplate is smaller.
  • Applying the 75 percent appliance factor to the range, dryer, or HVAC. It covers the other fixed appliances, and only when there are four or more.
  • Using 120 V as the service voltage, which doubles the calculated amperes. A typical dwelling service is 120/240 V, and the amps are figured at 240 V.
  • Using the optional method without checking eligibility. It can produce a lower figure, but it is not a shortcut unless the dwelling meets the 220.82 conditions.
  • Screening an old 60 or 90 A service against the calculated load alone. The 100 A minimum governs a one-family dwelling.
  • Entering the EV charger at nameplate. It is a continuous load and counts at 125 percent.

Frequently Asked Questions

How do I calculate the electrical load of a house?
Multiply the habitable area by 3 VA per square foot, add 1,500 VA for each small-appliance and laundry circuit, apply the lighting demand factors, then add the range, dryer, appliances, and the larger of heating or cooling under their own factors. Divide the total VA by 240 to get amperes. A 2,000 ft² all-electric house typically lands between 100 and 150 A depending on the method.
What size service does a 2,000 square foot house need?
It depends on the appliances, not just the area. With an electric range, dryer, water heater, and 10 kW of heat, the standard method gives about 33,000 VA — a 150 A service — while the optional method gives about 25,300 VA, supporting 110 A. A gas-appliance house of the same size can calculate far lower, though never below the 100 A minimum.
Can I use the optional method for any house?
No. The optional method is code-recognized only when the dwelling meets the 220.82 eligibility conditions, including a 100 A or larger service at the covered voltages. The arithmetic can be shown for any inputs, but eligibility has to be verified before the result is used for service sizing.
Can my existing 100 A service handle an EV charger?
Run the calculation with the charger at 125 percent of its rating. A 9.6 kW charger adds 12,000 VA — 50 A at 240 V — which pushes many homes past 100 A. The optional method, a smaller charger, or an approved load-management system that limits charging when the house is loaded are the usual ways to stay within an existing service.
Why does a 90 A service fail when my calculated load is only 80 A?
Because the code sets a 100 A minimum service for a one-family dwelling regardless of the calculated load. The screen runs against the larger of the calculated amperes and 100 A, so anything below 100 A is undersized on the minimum, not on the load.
Why is the service current figured at 240 V and not 120 V?
A typical one-family dwelling service is 120/240 V single-phase, and the service current is the total VA across the two ungrounded conductors at 240 V. Using 120 V doubles the amperes and oversizes the service.
Can I use this for a 208Y/120 V or three-phase service?
No. This calculator covers single-phase 120/240 V services for one-family dwellings. Three-phase and 208Y/120 V services use different voltage bases and demand tables. For those configurations, use a three-phase load calculation following NEC Article 220 Part IV or a specialist tool for the system type.
Does this size the wire, breaker, and neutral too?
No. It produces the calculated load and the minimum service rating. The neutral has its own NEC calculation, and conductor and overcurrent sizing follow from the load under their own rules — the service-entrance, wire-size, and breaker calculators cover those steps.

Frequently Used Together

Engineers often use these calculators in combination for complete project workflows:

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Service Entrance Size Calculator

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