Whole-Home Electrical Load Calculator: Service Size in Amps
Before you add an EV charger, a heat pump, or any large appliance, the question is always: does my electrical service have room for it? Most homes are served by 200-amp panels — some older homes still have 100A or 150A — and each circuit draw counts against that total. This calculator estimates your home's total connected load and, using a simplified NEC-style demand factor calculation, shows how many amps your service is likely drawing under typical conditions and how much headroom remains. Note: This is a planning estimate, not a substitute for a licensed electrician's load calculation. A qualified electrician can assess your actual panel, wire gauges, and local code requirements before any major additions.
Typical value: 3,000–6,000 W for a 1,500–3,000 sq ft home.
Typical 3-ton central AC: ~3,500 W. Heat pump similar.
Typical electric range: 8,000–12,000 W.
Level 2: 7,200 W (30A @ 240V) is typical. Set to 0 if not applicable.
sum of all loads before demand factor
NEC simplified: first 10 kW at 100%, remainder at 40%
demand load ÷ 240V service
Your 200A service has 127 amps of headroom.
Results update live as you type. For planning and field-check estimates — always verify against applicable standards and equipment ratings.
How home electrical load and service headroom are calculated
This calculator uses a simplified version of the NEC (National Electrical Code) residential load calculation method. The first step is totaling all connected loads — the maximum wattage of each circuit or appliance that could be drawing power. That sum is your total connected load.
Because not every load runs at full power simultaneously, the NEC applies a demand factor: the first 10,000 watts are counted at 100%, and any watts beyond that are counted at only 40%. This reflects statistical reality — your range, dryer, water heater, and EV charger rarely all run at full power at the same instant. For example, a home with 26,500 W of connected loads would calculate as: 10,000 + (16,500 × 0.40) = 16,600 W of demand load.
Converting demand load to amps uses Ohm's law: amps = watts ÷ volts. For a standard 240V residential service, 16,600 W ÷ 240V = 69.2 amps. Service headroom is simply the panel's rated ampacity (100A, 150A, or 200A) minus the calculated amps drawn.
Electricians performing a formal NEC load calculation also account for specific rules around largest motor loads, HVAC sizing, and additional circuits. This calculator provides a useful planning estimate — if your calculated load is close to or over your service size, that's a strong signal to consult a licensed electrician about a panel upgrade before adding any new large loads.