Current Calculator (Amps)

Electric current is the rate at which charge flows, measured in amperes (amps). This calculator finds it from voltage and resistance, from power and voltage — for DC, single-phase AC or three-phase AC with a power factor — from power and resistance, or from charge and time. It estimates running current from electrical input power; equipment ratings and installation requirements need separate checks.

How to use this tool

1. Pick the method that matches what you know.
2. Enter the voltage, resistance, power, or charge and time that the method needs; other boxes are ignored.
3. For AC loads, enter the power factor from the nameplate (use 1 for heaters and kettles).
4. For three-phase, enter the line-to-line voltage, such as 400 V or 480 V.
5. Read the current and the related values below it.

Formula

I = V ÷ R · I = P ÷ V · I = P ÷ (V × PF) · I = P ÷ (√3 × V_LL × PF) · I = √(P ÷ R) · I = Q ÷ t

P is real power in watts, V the voltage (RMS for AC), PF the power factor between 0 and 1, V_LL the voltage between two phase conductors, and Q the charge in coulombs that passes in t seconds. One ampere is one coulomb per second — about 6.24 × 10¹⁸ electrons every second.

Example

A three-phase motor taking 10 kW of real electrical input on 400 V with a power factor of 0.85 draws I = 10,000 ÷ (1.732 × 400 × 0.85) ≈ 16.98 A in each line. Its apparent power is about 11.76 kVA.