calcs.homes
calcs.homes
Estimate your home's electrical service size using the NEC 220.82 Optional Method — a simplified, widely used calculation for single-family dwellings. This follows US NEC conventions (120/240V split-phase) and isn't applicable to other electrical codes.
Estimate only — have a licensed electrician verify before upgrading or installing service.
General loads — lighting at 3 VA per square foot, small appliance and laundry circuits at 1,500 VA each, and the nameplate watts of your range, dryer, and other fixed appliances — are added together. The first 10,000 VA of that sum counts at 100%, and everything above it counts at only 40%. Heating or cooling load (whichever is larger) is added on top at full value, the total is divided by 240V for amps, and we round up to a standard service size: 100A, 150A, 200A, or 400A.
The 40% demand factor above 10,000 VA is how the National Electrical Code's 220.82 Optional Method avoids oversizing a service based on every circuit's nameplate rating — in practice, a home never draws its lighting, laundry, range, and dryer loads simultaneously at full power. Rounding up to a standard service size rather than an exact amperage matters because panels and breakers are only manufactured in set increments.
It follows the NEC 220.82 Optional Method, a real and commonly used calculation, but only a licensed electrician pulling a permit can perform an official load calculation for your specific home and local amendments.
Many electricians recommend 200A even when 100A meets code minimum, since it leaves headroom for a future EV charger, hot tub, or additional AC — upsizing during a planned upgrade is far cheaper than doing it again later.