What this converter does
This converter finds the current a load draws from its power in watts, for single-phase and three-phase circuits. Enter the voltage and power factor, pick the phase, and read the amps — handy for sizing cables and breakers. Swap the arrow to go from current back to watts.
Current is power divided by voltage times power factor; three-phase divides by an extra √3. Use a power factor of 1 for resistive loads. For power in kilowatts, see the kW to Amps converter.
The units it covers
Current from watts depends on the phase, the voltage and — for AC — the power factor.
View all units & their values
| Unit | Symbol | Value | Mainly used |
|---|---|---|---|
| Real power | W | P | Useful power delivered |
| Current | A | I | Amperes drawn from the supply |
| Voltage | V | V | Line-to-line for three-phase |
| Power factor | PF | cos φ | 1 for resistive; under 1 for motors |
The formula
Current is power divided by voltage times power factor:
A = W ÷ (V × PF) (÷ √3 more for three-phase)Where:
- W = the power you typed, in watts
- V = supply voltage (line-to-line for 3-phase)
- PF = power factor, 1 for resistive loads
Worked example
A single-phase 230 V load of 2,300 W runs at a power factor of 1. Find the current.
A = W ÷ (V × PF)2,300 ÷ (230 × 1) = 10 AThe circuit draws 10 A — size the cable and breaker above this figure.
The units in this example
The useful power the load consumes, in watts. Divided by voltage and power factor it gives the current; three-phase divides by an extra √3.
- A = W ÷ (V × PF) — 1ph
- A = W ÷ (√3 × V × PF) — 3ph
- 1,000 W = 1 kW
- resistive load: PF = 1
The amperes drawn from the supply. Cables and circuit breakers are rated in amps, so this is what you size the wiring to.
- 2,300 W at 230 V, PF 1 = 10 A
- W = V × A × PF — 1ph
- 1 A = 1 coulomb per second
- always size protection above the draw
FAQ
Sources
US DOE — estimating energy use · US EIA — electricity basics