Electrical load calculator: does your panel have room?

The standard method comes from Article 220 of the National Electrical Code: 3 VA per square foot of living area plus 1,500 VA per required kitchen and laundry circuit (with a demand factor above 3,000 VA), the range and dryer at their NEC demand values, the larger of heating or cooling, fixed appliances at 75% when you have four or more, and a 25% adder on the largest motor. Divide the total by 240 volts and you have the minimum service amperage. Our calculator walks those exact steps — enter nameplate ratings and it does the code math live.

The NEC minimum for a single-family dwelling is 100 amps (NEC 230.79(C)). A typical 2,000 sq ft home with an electric range, dryer, and water heater calculates to roughly 118 amps — which is why 125–200 amp services are the modern norm. All-electric homes with heat pumps, EV charging, and a spa often calculate past 200 amps, and that's where load management or a service upgrade conversation starts.

Every appliance has a nameplate — a metal plate or sticker, usually near the door frame, back panel, or base — listing watts (W) or kilowatts (kW). If the label only shows amps, multiply volts × amps to get watts: a 240 V appliance drawing 15 A is 3,600 W. Enter 0 for anything gas; gas appliances draw no meaningful electrical load in this calculation.

Not automatically — that's the most common false alarm in EV quotes. The 2023 NEC counts an EV charger at its full continuous rate (minimum 7,200 VA, per NEC 220.57), and on paper that pushes many 100–125 amp homes over. But a load calculation often shows a 32-amp charger fits fine, and when it doesn't, a smart panel or load-management device can pace charging around your other loads instead of an $8,000–$16,000 service upgrade. Run the calculator with the EV planning toggle, then let us verify with the formal calculation.

No. It uses the real NEC 220 standard-dwelling method, so it's a genuinely useful planning estimate — but the binding calculation is performed by a licensed electrician against your actual nameplates, local code amendments (WAC 296-46B in Washington), and utility requirements, and panel work requires a permit and inspection. Eco runs the on-site load assessment across Seattle, Everett, and Mount Vernon and gives you the math in writing.

A practical starting point is about 80% of your calculated load — the calculator suggests a standard generator size on that basis. Real-world sizing must also account for motor starting (inrush) current from well pumps, A/C compressors, and pool equipment, plus whether a load-management system lets a smaller unit cover the whole home. A generator sized only to the calculated load can nuisance-trip on big motor starts, so treat the suggestion as the beginning of the sizing conversation.