Electrical Load Calculator

Calculate your total wattage and amperage to ensure you don't overload your household circuit breakers.

Select Circuit Breaker Size (120V)
Appliance
Watts
Quantity
Total Load
0W
Total Current
0.0A
Circuit Status SAFE (0%)

Watt's Law & The 80% Rule

Watt's Law states that Power (Watts) = Voltage (Volts) × Current (Amps). In North America, standard wall outlets run on 120 Volts.

The 80% Continuous Load Rule: The National Electrical Code (NEC) dictates that a circuit breaker should only be loaded to 80% of its maximum capacity for continuous loads (anything running for 3 hours or more).

  • 15 Amp Breaker: Max capacity is 1800W. Safe continuous load is 1440W.
  • 20 Amp Breaker: Max capacity is 2400W. Safe continuous load is 1920W.

If you plug a 1500W space heater and a 1000W microwave into the same 15A circuit, you will trip the breaker immediately (2500W > 1800W)!