Electrical Load Calculator

These are starting points. Always check the nameplate on the actual equipment. A "1500W space heater" might actually draw 1,440W, close enough for estimation, but the nameplate is the legal number for code calculations. To translate those nameplate watts into a monthly utility cost per appliance, our appliance electricity cost guide ranks the typical household energy hogs by annual spend.

The National Electrical Code gives you two legitimate ways to size a dwelling service, and they routinely land on different numbers. The standard method (Article 220, Part III) factors each load category on its own. The optional method (NEC 220.82) is the shortcut this calculator uses. Here is how each one treats the same dwelling loads.

Neither method is "more correct." The optional method is usually lower for an all-electric home and is faster to run, which is why electricians reach for it on service upgrades. The standard method is what you fall back on when a dwelling sits outside the 220.82 eligibility window, such as a service below 100 A. For a permit, your local jurisdiction decides which calculation it wants to see.

The standard method walks each load category through its own demand factor. Here is the dwelling sequence, with the 2023 section numbers and the 2020 numbers where Article 220 was renumbered.

1. Add the general lighting and receptacle load. Multiply the living area by 3 VA per sq ft (NEC 220.41, Table 220.12 in 2020), then add 1,500 VA for each small-appliance and laundry circuit (220.52).
2. Apply the lighting demand factor. Table 220.45 (Table 220.42 in 2020) takes the first 3,000 VA at 100%, the portion from 3,001 to 120,000 VA at 35%, and anything above 120,000 VA at 25%.
3. Size the electric range. A single range up to 12 kW counts as 8 kW under Table 220.55, Column C. Ranges above 12 kW add 5% to that 8 kW for each kW over 12.
4. Apply the fixed-appliance demand factor. Four or more fastened-in-place appliances (water heater, dishwasher, disposal, and the like, but not the range, dryer, heat, or A/C) get a 75% factor under 220.53.
5. Count heating or cooling, not both. Heating and A/C rarely run together, so 220.60 lets you drop the smaller of the two. Fixed electric heat counts at 100% (220.51); the larger figure is the one you keep.
6. Total and convert. Add the demand-adjusted categories, divide by 240 V for amps, and round up to the next standard service size.

This calculator does not run those category steps. It applies the NEC 220.82 optional method instead: the first 10 kW of your total at 100% and the rest at 40%. That is a recognized code calculation for dwellings on a 100 A or larger service, not a rough shortcut. For an exact optional-method result the heating and A/C load is handled separately under 220.82(C); the tool folds everything into the one factor, so it slightly overstates an all-electric home with large electric heat. For a permit, a licensed electrician runs the full Article 220 numbers for your jurisdiction.

Once you have a demand figure, the service size is mostly arithmetic: divide demand by 240 V and round up to the next standard rating. The table below is engineering guidance from that arithmetic plus the standard ratings in NEC 240.6(A), not a code table you read a required size straight out of. A one-family dwelling can never go below 100 A (NEC 230.79(C)).

Leave headroom. A panel running near its calculated limit has no room for the next upgrade, and an electric vehicle charger or heat pump can erase a comfortable margin fast. If you are planning battery backup for these loads during an outage, the UPS battery backup calculator shows how long a bank would carry the demand.