Watts to Amps Calculator
Convert power in watts to current in amps for AC or DC circuits.
Please note: For planning and educational use only. Electrical installation is governed by wiring regulations and is dangerous when done incorrectly. Always have work designed, installed and inspected by a qualified electrician.
What the Watts to Amps Calculator does
Current is power divided by voltage, adjusted for power factor on AC circuits and by √3 on three-phase supplies. It determines cable size and breaker rating, so getting it right is a safety matter rather than a convenience.
Formula
DC: I = P ÷ VAC single phase: I = P ÷ (V × PF)AC three phase: I = P ÷ (√3 × V × PF)
Inputs explained
| Input | Unit | Required | Notes |
|---|---|---|---|
| Supply type | one of 3 options | Yes | — |
| Power | W | Yes | Accepts more than 0. |
| Voltage | V | Yes | Accepts more than 0. |
| Power factor | number | In some modes | Accepts 0.01 or more, up to 1. Shown Supply type is AC single phase, or Supply type is AC three phase. |
How to use it
- Choose Supply type.
- Enter Power and Voltage.
- Fill in the remaining inputs the form shows for your choice.
- Select Calculate.
Worked example
A 2,000 W load on a 230 V single-phase supply at 0.95 power factor.
- Supply
- AC single phase
- Watts
- 2000
- Voltage
- 230
- Power factor
- 0.95
I = 2000 ÷ (230 × 0.95) = 9.15 A, suggesting a 16 A breaker with continuous-load headroom.
Frequently asked questions
Why does power factor matter here?
On AC circuits the current can be higher than real power alone suggests, because reactive current still flows through the cable and must be carried.
Why size a breaker at 125% of the load?
Continuous loads running over three hours are limited to 80% of the breaker rating, which is the same thing expressed the other way round.
Method and sources
Method. Current from power and voltage — I = P ÷ V for DC, I = P ÷ (V × PF) single-phase AC, and I = P ÷ (√3 × V × PF) for three phase.
Applies to. None for the arithmetic; conductor and device selection is governed by national wiring regulations
Assumptions
- The power factor entered describes the load; a purely resistive load has a power factor of one.
Limitations
- Motor and electronic loads draw well above their running current at start-up, and this figure describes steady state only.
- The result is a current, not a conductor or protective-device size. Those depend on installation method, grouping, ambient temperature and the regulations in force.
Sources
- The national wiring regulations applying where the installation is located — Varies by country. Everything about sizing a circuit from this current, which the calculator deliberately does not do.