Residential Load Calculator

How it’s calculated. NEC 220.82 optional method for a 120/240 V single-phase dwelling. General load = 3 VA/ft² + 1,500 VA per small-appliance circuit (minimum 2) + 1,500 VA per laundry circuit + the nameplate VA × quantity of every fastened-in-place appliance (and EV supply equipment). Demand is then 100% of the first 10 kVA + 40% of the remainder. Per 220.82(C) it then adds the larger of air conditioning/cooling (100%) or heating — heat pumps count on both sides, and electric heat is taken at its demand factor. Service amps = total VA ÷ 240, rounded up to the next standard size. The worked calculation above mirrors the line-by-line format an AHJ expects on a load sheet — click Copy to paste it into your plans.

A/C size is the motor load (MCA), not the breaker. The amps shown next to each tonnage are the MCA (minimum circuit ampacity) from the nameplate — that is the figure used in the load calculation (VA = MCA × 240). It is not the breaker size. The breaker is the nameplate MOCP (max overcurrent protection / max fuse-HACR breaker), which is larger — a 4-ton split (~26 A MCA) typically carries a nameplate MOP around 35–40 A and a 5-ton (~32 A MCA) around 45–50 A, though it varies by manufacturer and model. The breaker figure this tool exports is an estimate only — MOP is a nameplate maximum, so always read it off the unit rather than calculating it. Use the MCA here, and use the nameplate MOCP for the breaker on the panel schedule. Heat pumps are sized by tonnage/MCA (the value is VA), not heating kW. EV charging is in the general-load bucket per the optional method; some jurisdictions EV supply equipment is calculated per NEC 220.57 at the larger of 7,200 VA or the nameplate rating, and this tool applies that floor to the service calculation. AHJs differ on whether the 220.82(B) 40% demand factor may then be applied to it — confirm locally. Note the floor is a service-calculation rule only: the branch circuit is still sized from the actual nameplate, so a 16 A charger remains a 20 A circuit.

Solar & battery (Power Wall). Solar PV and battery storage are sources, not loads — they do not reduce the calculated service load (you still size the service for the loads). What they do require is the separate NEC 705.12 interconnection (“120% busbar rule”) check that this tool runs: the main breaker plus the PV and battery backfeed breakers (each at 125% of inverter output) must stay within 120% of the panel busbar rating. That result is shown as its own block in the worked calculation — the figure a solar/Power Wall permit needs.

Backup generator. A backfed generator is also a source, not a load. The tool reports its output current (single- or three-phase) and the backfed breaker size. A portable generator typically lands on a 30 A (L14-30), 40 A, or 50 A (14-50) inlet and a matching backfed breaker, held against the main by an interlock kit so the generator can never feed the utility. Many DIY setups back-feed a subpanel (a “generator load center”) holding the storm circuits rather than the main — pick that panel above and the backfed breaker is added to that panel’s schedule. The backfed breaker needs a hold-down per 408.36; because an interlock/ATS is a non-parallel transfer, the 705.12 120% rule does not apply. A generator smaller than the calculated load is normal (load management or selected backup circuits).

Detached garage / outbuilding is calculated as its own feeder (3 VA/ft² plus its appliance list) and also rolled into the dwelling service total — so the plans show how the load balances.

Please note. Arizona Electrical Solutions is a commercial & industrial design-build contractor, and this calculator is a free educational resource. Always verify against the current NEC and your local amendments, and have a licensed electrician confirm any service sizing.