Electrical Load Calculator Formula

Understand the math behind the electrical load calculator. Each variable explained with a worked example.

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Formulas Used

Current Draw

amps = voltage > 0 ? total_watts / voltage : 0

With Safety Factor

amps_with_safety = voltage > 0 ? total_watts / voltage * safety_factor / 100 : 0

Recommended Breaker

breaker_size = voltage > 0 ? ceil(total_watts / voltage * safety_factor / 100 / 5) * 5 : 0

Variables

VariableDescriptionDefault
voltageVoltage(V)120
total_wattsTotal Watts(W)1500
safety_factorSafety Factor(%)125

How It Works

Electrical Load Formula

Amps = Watts / Volts

NEC Safety Factor = 125% (for continuous loads)

Breaker sizes are standard: 15A, 20A, 30A, 40A, 50A. Always round up to the next standard size.

Worked Example

1,500W load on a 120V circuit with 125% safety factor.

voltage = 120total_watts = 1500safety_factor = 125
  1. 01Amps = 1,500W / 120V = 12.5A
  2. 02With safety = 12.5 × 1.25 = 15.6A
  3. 03Recommended breaker = 20A

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