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Select a calculation method, then enter the connected loads from the project plans and specifications to determine the required service size per NEC 2026 Article 120. Not sure which? Start with the Optional Method (NEC 120.82): it fits most single homes with a 100 A or larger service. Use the Standard Method when the Optional Method does not apply or your plan checker asks for it.

The Optional Method allows a simplified calculation for single  dwelling units served by a single 120/240V or 208Y/120V, 3-wire set of service or feeder conductors with an ampacity of 100A or greater (NEC 120.82(A)). It totals general and fixed loads, applies 100% to the first 8 kVA and 40% to the remainder, and then adds the larger of the heating or cooling load per NEC 120.82(C).

Code editionNEC 2023NEC 2026 New

NEC 2026: load calculations are in Article 120 (formerly Article 220). Use it only where the 2026 NEC is adopted.

NEC Load Calculator (Single Family Using Optional Method)
Unit Details
Building
Note: Floor area is calculated from outside dimensions, excluding open porches and unfinished areas not adaptable for future use as a habitable room or occupiable space. NEC 2026 §120.5(C): attached garages are included; detached garages are excluded.
Small-Appliance & Laundry Circuits
1,500 VA per circuit (NEC 120.82(B)(2)).
Kitchen, dining, pantry. Min. 2.
Min. 1.
Fixed Appliances
Nameplate VA. Enter 0 if not installed.
Other Appliances
Pool pump, well pump, spa, etc. Nameplate VA.
Cooking, Laundry & Water Heating
Nameplate VA (kW × 1000).
Do not use Table 120.55 values.
California50A, 240/208V labeled circuit for future range (2025 Energy Code).
California30A, 240/208V labeled circuit for future dryer (2025 Energy Code).
California30A, 240/208V labeled circuit for future water heater (2025 Energy Code).
Heating & Cooling
The larger of heating or cooling is used (NEC 120.82(C)).
Condensing unit or heat pump. 0 if none.
AHU/FCU fan motor only (excludes supplemental heat).
Total nameplate kW.
4 or more: 40%. Fewer: 65%.
EV Charging
Counted at 100% (no demand factor).
Use charger nameplate if installed.
California40A, 208/240V EV circuit (CALGreen 4.106.4) = 9,600 VA.
*Reference: California Electric Readiness fact sheet (PDF)