Electrical Load Calculator

The nameplate on the actual equipment is the number the worksheets ask for; Placer converts nameplate watts to volt-amperes at 1:1. To translate those nameplate watts into a monthly utility cost per appliance, our appliance electricity cost guide ranks the 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." On the all-electric house of the first worked example below, the optional method gives the smaller service, and it takes fewer steps. 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. Take the range at the demand value of Table 220.55, or at its nameplate where your own form asks for it. The optional-method worksheets on this page take it at nameplate (Sacramento: "Range (NPR - nameplate rating)").
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 is counted at the factor the code's standard method sets for it; 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.

Cited to NEC Table 220.45 and Table 220.55. The code text itself is not freely available to link; confirm the figure against the current edition or your authority having jurisdiction before acting.

This calculator does not run those category steps. It runs the optional method as the worksheets print it: the factor of 10,000 VA at 100 percent and the rest at 40 percent applies to lines 1 to 4 only, and Huntington Beach's form says of its appliance box, "Do not include any heating or air-conditioning equipment in this section." The heating and air-conditioning line and the EV charger line are added after the factor. For a permit, your own authority's worksheet governs.

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)). This calculator holds its result to that floor as three of the municipal worksheets print it: Huntington Beach (capture sha256 1464749897d7) prints "9. Minimum Size Service or Feeder 240.6(A) ... (minimum is 100 amperes)", and the Sacramento (capture sha256 a8d74f62155d) and Rialto (capture sha256 eacba9822122) worksheets print "2025 CEC 220.82 (100 AMP Minimum)". Where the next standard overcurrent rating is under 100 A, the result shows 100 A and names those three forms. On 1,000 sq ft with the two small-appliance circuits and one laundry circuit the forms print as minimums and nothing else, the load is 7,500 VA and 31 A; the next standard overcurrent rating is 35 A, so the result shows 100 A. Florence's existing-dwelling worksheet (capture sha256 86048b21dc2d) prints "service entrance or feeder conductors with an ampacity of 100 or greater" as the scope of its method, not as a minimum rating, and the Placer, Maricopa and Campbell worksheets print no minimum.

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.