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 — for example a 4-ton split (~26 A MCA) is commonly on a 50 A breaker and a 5-ton (~32 A MCA) on a 60 A breaker. 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 require EVSE at 100% per 625.42 — confirm locally.

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.