Free Electrical Calculators

NEC-based tools for working electricians and exam prep. All calculators are free - no signup required.

Calculate conduit fill percentage per NEC Chapter 9. Select conduit type, size, and wire configuration to verify code compliance.

Calculate voltage drop for any circuit. Verify compliance with the NEC 3% branch circuit and 5% total drop recommendations.

Convert between watts, amps, volts, kW, kVA, and horsepower. Supports single-phase and three-phase calculations.

Calculate electrical box fill per NEC 314.16. Add conductors, clamps, devices, and grounds to verify box capacity.

Determine the correct breaker size for your circuit. Accounts for continuous and non-continuous loads per NEC 240.6(A).

Calculate voltage, current, resistance, and power using Ohm's Law. Enter any two values to find the other two.

Find the right wire size for your circuit. Accounts for ampacity, temperature derating, bundling, and voltage drop.

Interactive NEC Table 310.16 ampacity chart. Filter by material, insulation type, and temperature rating.

Apply NEC temperature correction and conductor bundling adjustment factors to find derated ampacity.

Size transformers and calculate overcurrent protection per NEC 450.3(B). Includes primary and secondary breaker sizing.