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Watts to amps calculator

Enter the power in watts and see straight away how many amps an appliance draws. Choose DC, single-phase AC or three-phase; if you leave the voltage empty we use 230 V, or 400 V for three-phase.

What do you want to know?
Type of current

In watts; 2.3 kW works too.

In amps.

In volts. Empty = 230 V (UK, Europe), or 400 V for three-phase. In the US it is 120 V.

Empty = 1 (heaters, lamps). Motors and power supplies: 0.8 to 0.95.

Fill in the fields; the answer appears here straight away.

How it works

  1. Enter the values

    Type the numbers or the formula. Decimals may use a point or a comma. No idea? Click Fill in an example.

  2. Instant answer

    The answer appears as you type, with the most important intermediate values.

  3. See the working

    Under "How it's worked out" you see the steps, handy for checking your own calculation.

How to convert watts to amps

Current follows from power and voltage:

  • DC: I = P ÷ U
  • Single-phase AC: I = P ÷ (U × cos φ)
  • Three-phase AC: I = P ÷ (√3 × U × cos φ), where U is the voltage between two phases (400 V)

A 2300 W kettle on 230 V draws 2300 ÷ 230 = 10 A. As a rule of thumb, 1000 W on 230 V is about 4.3 A. On a 120 V supply, as in the US, the same 1000 W is 8.3 A: type 120 in the voltage field.

Watts and amps at 230 V (single phase, cos φ = 1)

Power Current
100 W 0.43 A
500 W 2.17 A
1000 W 4.35 A
2000 W 8.70 A
3000 W 13.04 A
3680 W 16 A

So a 16 A circuit can deliver about 3680 W. If several appliances share one circuit, add up their power.

What is cos φ?

With AC, the current in motors, transformers and power supplies doesn't peak at exactly the same moment as the voltage. That lag is the power factor (cos φ). For heaters and incandescent bulbs it is 1; for motors it is often between 0.8 and 0.9. A lower power factor means more current for the same power. If you leave the field empty, we use 1.

Fuses and cables

The tool shows the next standard breaker size (6, 10, 13, 16, 20, 25, 32, 40, 50 or 63 A). Treat this as a guide: the right breaker and cable size also depend on cable length, how it is installed and the type of load. Leave changes to your installation to a qualified electrician.

Need the other direction? Use amps to watts. To see what an appliance costs to run, try the electricity cost calculator.

Examples beyond the kettle

Load Power Supply Current
EV charger 11 kW 3 phases, 400 V 15.9 A per phase
EV charger 22 kW 3 phases, 400 V 31.8 A per phase
Space heater 1500 W 120 V 12.5 A
Phone charger 20 W 5 V DC 4 A

The 11 kW charger is calculated as 11,000 ÷ (√3 × 400) ≈ 15.9 A, which is why a 16 A three-phase connection carries it.

Continuous loads in the US

A 15 A breaker on 120 V is rated for 1800 W, but a continuous load should stay under 80% of that: 12 A, or 1440 W. A 1500 W heater is therefore slightly over what that circuit should carry continuously. For the cost of running it, use the electricity cost calculator.

Fuses and cables

The calculator suggests the next standard breaker size. Treat it as a guide: cable length, installation method and load type decide the real choice, and changes to your installation belong with a qualified electrician.

Frequently asked questions

How many amps is 1000 watts?

At 230 V, about 4.35 A. At 120 V, as in the US, 1000 W is 8.33 A. The lower the voltage, the more current the same power needs.

How do I know if a circuit is overloaded?

Add up the power of everything that runs at the same time and divide by the voltage. A 16 A circuit on 230 V carries at most 3680 W, so a kettle (2300 W) plus a heater (2000 W) is already over the limit.

What power factor should I enter?

Leave the field empty (cos φ = 1) for heaters, kettles and incandescent bulbs. For motors and many power supplies use 0.8 to 0.95, which raises the current for the same power.

When do I choose three-phase?

For equipment connected to three phases, such as a heat pump, an induction hob or an EV charger. The answer is the current in each phase, with U the voltage between two phases.