What NEC method does this calculator use?

It uses the NEC Article 220 Standard Method for Dwelling Units (220.82 is the optional method; this tool applies 220.52–220.55 demand factors including the 3 VA/sq ft general lighting load, small-appliance and laundry circuits, and the NEC Table 220.55 demand factors for cooking equipment).

Why is only the larger HVAC load counted?

NEC 220.60 (Non-coincident Loads) lets you omit the smaller of two loads that are never used at the same time — in most homes, heating and cooling are mutually exclusive, so only the larger is included in the calculation.

What are the standard residential service sizes?

Common residential service ratings are 100 A, 150 A, 200 A, 320 A (two 200 A), and 400 A. Most modern homes need at least 200 A, especially with EV chargers, heat pumps, or electric cooking. Utility companies typically offer 100 A, 150 A, and 200 A as standard options.

How is the general lighting load calculated?

NEC 220.12 assigns 3 VA per square foot of living area for general lighting. For a 2,000 sq ft home that is 6,000 VA. A demand factor from NEC Table 220.42 then applies: first 3,000 VA at 100%, next 120,001 VA (up to 3,000 VA) at 35%. For most homes only the 100% and 35% tiers matter.

Does this calculator cover commercial buildings?

This tool is designed for one- and two-family dwellings per NEC Article 220 Part III. Commercial buildings use different occupancy-based unit loads from NEC Table 220.12 and different demand factors — consult NEC Article 220 Part IV or a licensed electrician for commercial calculations.

What voltage is used for the amperage calculation?

The service amperage is calculated at 240 V single-phase (standard North American residential service): Amps = Total VA ÷ 240. The result is then rounded up to the nearest standard service size.

Electrical Service Load Calculator

Name: Electrical Service Load Calculator
Availability: InStock
Author: Nham Vu

Enter your building's square footage, appliances, and HVAC loads to calculate the total service load and minimum panel amperage per NEC Article 220.

Building & Loads

General Lighting (NEC 220.12)

Conditioned Floor Area (sq ft)

@ 3 VA/sq ft — demand factors applied per NEC Table 220.42

Small Appliance & Laundry (NEC 220.52)

Small Appliance Circuits

Min 2 required

Laundry Circuit

Yes No

1,500 VA

Fixed Appliances (watts)

Range / Oven (W)

Clothes Dryer (W)

Water Heater (W)

Dishwasher (W)

Other Fixed Appliances (W)

Garbage disposal, spa, EV charger, etc. (if 4+ fixed appliances, 75% demand factor applies)

HVAC — Largest Load Only (NEC 220.60)

Heating (W)

Air Conditioning (W)

Only the larger value is included (non-coincident loads).

Enter building details on the left and click Calculate.

Summary

Enter your building's square footage, appliances, and HVAC loads to calculate the total service load and minimum panel amperage per NEC Article 220.

How it works

Enter the conditioned floor area of the building in square feet.
Add small-appliance circuits (minimum 2 required by NEC 220.52(A)).
Add laundry circuit if present (NEC 220.52(B)).
Enter wattage for fixed appliances: range, oven, dryer, water heater, dishwasher.
Enter the larger of heating or cooling loads for HVAC (NEC 220.60 omits the smaller).
The calculator applies the NEC demand factors and shows total load in VA and required service amps.

Use cases

Size the main service panel for a new residential construction.
Verify whether an existing 100 A or 150 A service can handle planned additions.
Plan a service upgrade before adding an EV charger or heat pump.
Prepare load calculation documentation required for a permit.
Estimate panel capacity before purchasing a generator or transfer switch.
Check NEC Article 220 compliance for an inspector or utility company.

Frequently Asked Questions

Last updated: 2026-07-01 · Reviewed by Nham Vu