contractor · 2026-05-01

Residential electrical load calculator

Estimate total amperage demand using NEC standard load calculation method to size a residential service panel (100A vs 200A).

Service amps required
148
@ 240 V

Inputs

Heated living space (sqft)2,200
Small-appliance + laundry circuits3
Electric range (kW)12
Electric water heater (kW)4.5
Electric dryer (kW)5
Largest HVAC load (kW)8
EV charger (kW)7.7
Other fixed loads (kW total)2

Supporting metrics

Total VA demand35,540
General lighting + circuits VA11,100
Appliances VA (after demand factor)8,740
HVAC + EV VA (100% per NEC)15,700

About this calculator

NEC service-panel sizing — the optional method

Building inspectors size residential services using NEC 220.82 (the optional method) because the standard method overestimates real-world load. The optional method applies a demand factor — not every appliance runs full-tilt simultaneously — and treats HVAC + EV at 100%.

What the calc does

  1. General lighting + small-appliance circuits: 3 VA × heated sqft, plus 1,500 VA per small-appliance and laundry circuit (minimum 3 circuits per code).
  2. Appliances: nameplate kW for range, water heater, dryer, fixed loads.
  3. Demand factor: first 10,000 VA at 100%, everything above at 40% (optional method).
  4. HVAC + EV: full nameplate, no discount. EV charging especially counts at 100% because it can run alongside HVAC.

Total VA / 240 V = required service amperage. Round up to the next standard panel size: 100, 125, 150, 200, 320/400.

When 200A isn't enough anymore

Heat pumps + EV chargers are why new builds are spec'd at 200A or even 320/400A. A 1990s house with gas heat, gas range, and gas dryer fits in 100A easily. Add a heat pump (8 kW) and a 48A EV charger (11.5 kW) and you're suddenly looking at 60+ amps of "always at 100%" load on top of the rest of the house.

FAQ

Standard method vs optional method — which one applies?

NEC 220.82 (optional) is what virtually all residential calcs use because it produces realistic numbers. The standard method (220.40 series) gives a much larger total because it doesn't apply diversity factors. Inspectors accept either; optional is the default.

Does my dryer really pull 5 kW continuously?

Briefly, yes — heating elements run flat-out. But the demand factor in the optional method already accounts for the fact that your dryer, range, and water heater rarely all peak together. That's why the math discounts everything above 10,000 VA at 40%.

I plan to install solar — does that change my service size?

Generally no. Solar interconnection rules (NEC 705.12) cap how much solar you can backfeed through your existing panel based on busbar rating, but they don't change your load calc. You may need a panel upgrade anyway if the inverter rating exceeds 120% of your busbar.

Should I jump from 100A to 200A 'just in case'?

If you're already opening the meter base — yes. The marginal cost from 100A to 200A is usually $300-700 in materials; the cost to upgrade later (after walls are closed, drywall is finished, panel is full) is $2,500-5,000. EV + heat pump + induction range are all common upgrades that push 100A homes to 200A.