Electrical Load Calculator

Total load (watts) = sum of all appliance wattages. For amperage: amps = watts / voltage. For a 120V circuit: 1,000W / 120V = 8.33A. For a 240V circuit: 1,000W / 240V = 4.17A. This calculator handles both 120V and 240V loads.

The National Electrical Code (NEC) Article 220 defines load calculation methods for residential panels. A simplified method: calculate all loads (general lighting at 3VA/sq ft, small appliance circuits, laundry, and specific appliance loads), apply demand factors, and divide total watts by voltage (240V) to get required amperage. Most new homes use 200A service.

Not all loads operate simultaneously at full capacity. NEC demand factors allow you to reduce calculated loads: the first 3,000W of general lighting is counted at 100%, the next 117,000W at 35%, and so on. This means a 5,000 sq ft home won't actually draw maximum lighting load from every room at once.

Generator sizing follows similar logic to load calculation. Identify which loads you want to power simultaneously during an outage (essentials: refrigerator, sump pump, some lights, HVAC) and sum their running watts. Add 20-25% for safety margin and motor surge loads. A 7,500-12,000W generator covers most essential household loads.

Watts measure real power (doing work). Amps measure current. Volt-amps (VA) = volts x amps, which equals watts for purely resistive loads but exceeds watts for reactive loads (motors, transformers) due to power factor. For sizing breakers and wiring, use amps. For calculating energy use, use watts (or kWh).