Electrical Load Calculator
Estimate a home’s total electrical service load with the NEC standard method — general lighting demand plus appliances — and the service amps at 240 V.
How it works
general = ft² × 3 + small-appliance × 1500 + laundry × 1500 · general demand = 3000 at 100% + remainder at 35% · total VA = general demand + appliances + HVAC + range · amps = VA ÷ 240
The NEC standard method (Article 220) starts from a per-square-foot lighting allowance of 3 VA, adds the fixed small-appliance and laundry circuits, then applies a demand factor because not everything runs at once — the first 3,000 VA counts fully and the rest at 35%. Fixed appliances, the larger of heating or cooling, and the range are added, and the total is divided by the 240 V service voltage to get the amperage that sets the panel size.
Worked example
A 1,500 ft² home: general = 1,500 × 3 + 2 × 1,500 + 1,500 = 9,000 VA. Demand = 3,000 + (9,000 − 3,000) × 0.35 = 5,100 VA. Add 5,000 W fixed + 3,500 W HVAC + 8,000 W range = 21,600 VA total, ÷ 240 = 90 A — comfortably served by a 100 A panel.
Frequently asked questions
Standard method or optional method?
This uses the standard method, which is conservative and works for any dwelling. The optional method (Article 220.82) applies a flatter 40% factor above the first 10 kVA and often yields a smaller service; electricians choose whichever the code allows and the AHJ accepts.
Why 240 V and not 120 V?
Residential service in North America is split-phase 240/120 V, and the whole-house load is calculated across the full 240 V. Individual 120 V branch circuits draw from one leg, but the service capacity is figured at 240 V.
Is 200 A always enough?
For most homes, yes. Large houses, electric heat, EV charging and shop equipment can push past it, and the calculation — not a rule of thumb — is what tells you when to step up to 300 or 400 A.
Related calculators
Educational estimates only — electrical work must follow the National Electrical Code (NEC) and local amendments, and be done or inspected by a licensed electrician.