Does this calculator replace a permit-stamped load calculation?

No. It uses the NEC 220 standard method without demand factors to give a conservative estimate. Permit-stamped load calculations should be done by a licensed electrician.

Why 3 VA per sq ft for general lighting?

That’s the value in NEC 220.12 for dwelling units. It covers receptacles and lighting; the small-appliance and laundry branches are added separately.

What does the 25 % margin mean?

NEC 220.18 requires continuous loads to be served at 125 % of their value. We apply the same margin globally so the recommended service size leaves headroom — the next standard breaker size above 125 % of the calculated current.

How do I find an appliance’s wattage?

Check the nameplate inside the door or on the back of the unit. If only amps and volts are listed, multiply amps × volts to get watts.

Will this tell me whether to upgrade my panel?

It will tell you the minimum service size the connected load needs. If your existing service is smaller than the recommendation, talk to an electrician — but always confirm with a permit-stamped calc.

Electrical Load Calculator

Estimate total household load and recommended service amperage based on NEC 220 standard method.

Written by Golam Rabbani, Founder & Lead Engineer

This interactive tool requires JavaScript. Read the formula and worked example below; you can compute the result by hand.

How to use this electrical load calculator

Choose imperial (sq ft) or metric (m²) units.
Enter your dwelling’s floor area and select the service voltage (typically 240 V in the US).
Set the number of small-appliance circuits (kitchen) and laundry circuits — minimum 2 and 1 per NEC.
Edit the appliance list: each row takes a name, nameplate watts, and quantity.
Press Calculate to see total watts, amps at 120 and 240 V, and a recommended service size.

About this electrical load calculator

The electrical load calculator estimates the total connected demand of a dwelling using the NEC 220.12 standard method: 3 VA per sq ft for general lighting, 1,500 VA for each small-appliance branch circuit (NEC 220.52(A)), 1,500 VA for each laundry circuit (NEC 220.52(B)), and the sum of nameplate watts for fixed appliances. It then divides by the service voltage to get amps and applies a 25 % safety margin to recommend a service tier (100, 125, 150, 200 A, etc.).

Example: a 2,000 sq ft house with 2 small-appliance circuits, 1 laundry circuit, an 8,000 W range, a 4,500 W water heater, and a 5,000 W heat pump. General load = 2,000 × 3 = 6,000 W. Small-app = 2 × 1,500 = 3,000 W. Laundry = 1,500 W. Fixed = 8,000 + 4,500 + 5,000 = 17,500 W. Total = 28,000 W → 28,000 / 240 = 116.7 A. With the 25 % margin, the calculator recommends a 150 A service.

Note: the standard method does not apply NEC demand factors (which would reduce some loads). A licensed electrician should run the full Optional or Standard method per Article 220 before pulling permits.

FAQ

Does this calculator replace a permit-stamped load calculation?: No. It uses the NEC 220 standard method without demand factors to give a conservative estimate. Permit-stamped load calculations should be done by a licensed electrician.
Why 3 VA per sq ft for general lighting?: That’s the value in NEC 220.12 for dwelling units. It covers receptacles and lighting; the small-appliance and laundry branches are added separately.
What does the 25 % margin mean?: NEC 220.18 requires continuous loads to be served at 125 % of their value. We apply the same margin globally so the recommended service size leaves headroom — the next standard breaker size above 125 % of the calculated current.
How do I find an appliance’s wattage?: Check the nameplate inside the door or on the back of the unit. If only amps and volts are listed, multiply amps × volts to get watts.
Will this tell me whether to upgrade my panel?: It will tell you the minimum service size the connected load needs. If your existing service is smaller than the recommendation, talk to an electrician — but always confirm with a permit-stamped calc.