How to use the electrical load calculator
Service size drives panel location, feeder conduit and utility coordination. This tool walks through a simplified NEC Article 220 standard-method estimate for a one-family dwelling: general lighting from floor area, small-appliance and laundry circuits, demand factors, fixed appliances, the larger of heat or A/C, optional EV load, and a 25% largest-motor adder. Results are for education and early design — not a permit calculation.
- Enter conditioned / dwelling floor area in ft² or m².
- Confirm small-appliance and laundry circuit counts (NEC typically requires two SA and one laundry at 1,500 VA each).
- Add nameplate or typical VA for range, dryer, water heater and other fixed appliances.
- Enter A/C and heating VA — the tool keeps the larger — plus EV and largest motor if known.
NEC 220 standard-method formulas (simplified)
General lighting = 3 VA/ft² × area (or ≈ 33 VA/m² × area)
Small appliance = 1,500 VA × circuits · Laundry = 1,500 VA × circuits
Demand on (lighting + SA + laundry): first 3,000 VA @ 100%, remainder @ 35%
Fixed appliances (4 or more): often × 75% combined (simplified Table 220.53 style)
Range / dryer: use nameplate or typical demand values entered above
HVAC: take the larger of heating VA or cooling VA
Largest motor adder = 25% × largest motor VA
Service amps ≈ total VA ÷ 240 V (single-phase 120/240)
Recommend next standard size: 100 / 150 / 200 / 400 A
Typical presets: electric range 8,000 VA, dryer 5,000 VA, water heater 4,500 VA, 3-ton A/C ~3,600 VA. Replace presets with nameplate values when you have them. Gas appliances that only need ignition should be entered as 0 or a small VA.
| Total load (approx.) | Common service |
|---|---|
| ≤ 24 kVA | 100 A |
| 24–36 kVA | 150 A |
| 36–48 kVA | 200 A |
| > 48 kVA | 320 / 400 A class |
Worked examples
A 2,000 ft² three-bedroom house
Lighting = 2,000 × 3 = 6,000 VA. Two SA + one laundry = 4,500 VA. Subtotal 10,500 VA → demand = 3,000 + 0.35 × 7,500 = 5,625 VA. Add range 8,000, dryer 5,000, water heater 4,500, dishwasher/disposal 1,500 — four appliances → 75% × 19,000 = 14,250 VA. A/C 3,600 VA (no electric heat). Total ≈ 5,625 + 14,250 + 3,600 = 23,475 VA → 23,475 ÷ 240 ≈ 98 A → recommend 100 A service if no EV, or step to 150–200 A with margin.
Same house with a 48 A EV charger
A 11.5 kW EVSE continuous is entered as about 11,500 × 1.25 ≈ 14,400 VA for branch sizing; as a connected load adder in this simplified sheet we add 14,400 VA. Total climbs past 37 kVA → about 158 A → a 200 A service is the usual conversation with the electrician.
Metric 180 m² all-electric flat
Lighting ≈ 180 × 33 = 5,940 VA. Same SA/laundry demand path, heat-pump outdoor unit plus strip heat — take the larger (strips often win). Expect a 150–200 A single-phase service depending on cooking fuel and dryer.
Who this calculator helps
- Architects coordinating panel rooms, meter locations and utility upgrades in schematic design.
- Design-build and GC teams flagging 100 vs 200 A early so pricing is honest.
- Homeowners planning EV chargers, heat pumps or all-electric retrofits.
- Students learning the shape of an NEC 220 standard-method takeoff.
Practical tips
- Floor area ties to the square footage calculator; lighting design loads sit on the lighting calculator.
- Fixture counts for wet rooms are on the plumbing fixture calculator; occupancy-driven loads for other building types use the occupancy load calculator.
- Use nameplate FLA × voltage × √3 (three-phase) or × 1 (single-phase) when you have real equipment data.
- Continuous loads (EVSE, some heaters) need 125% on the branch-circuit sizing even when demand factors apply at the service.
- Local amendments and the optional method (220.82) can change the answer — ask the AHJ which path they want on the permit set.
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