How this calculator works
Watts are volts times amps, so amps are watts divided by volts. For loads with a power factor of 1 (kettles, heaters, filament bulbs) that is all there is to it. For loads with a lower power factor, divide by the power factor as well. In a three-phase supply, divide by 1.732 times the line voltage (400 V).
Worked example: a 3,000 W kettle on 230 V draws 13.04 A, which is just inside a 13 A plug, so it takes a 13 A fuse, and needs a circuit with an MCB of at least 16 A. A 2,000 W fan heater draws 8.70 A, a 60 W lamp 0.26 A (a 3 A fuse), and a 10.5 kW shower 45.7 A, which is too much for a plug. A 15 kW three-phase load at 400 V and a power factor of 0.9 draws 24.1 A per phase, and a 120 W load on 12 V DC draws 10 A.
Watts to amps on 230 V mains
Power factor 1, with the fuse for a 13 A plug.
| Watts | Amps at 230 V | Plug fuse |
|---|---|---|
| 100 W | 0.43 A | 3 A |
| 500 W | 2.17 A | 3 A |
| 690 W | 3.00 A | 3 A |
| 1,000 W | 4.35 A | 5 A |
| 1,150 W | 5.00 A | 5 A |
| 1,500 W | 6.52 A | 13 A |
| 2,000 W | 8.70 A | 13 A |
| 2,500 W | 10.87 A | 13 A |
| 2,990 W | 13.00 A | 13 A |
| 3,000 W | 13.04 A | 13 A |
| 3,600 W | 15.65 A | Too much for a plug: needs its own circuit |
| 7,500 W | 32.61 A | Too much for a plug: needs its own circuit |
| 10,500 W | 45.65 A | Too much for a plug: needs its own circuit |
Tips before you buy
- A 13 A plug is rated for 3,000 W at 230 V, but an appliance of more than that needs its own circuit. A 3 kW kettle draws 13 amps.
- Fit a 3 A fuse for appliances up to about 700 W (lamps, TVs, chargers), and a 13 A fuse for heaters, kettles and irons.
- A ring main normally has a 32 A MCB, which can supply 7,360 W in total across all its sockets: do not run several 3 kW heaters on one ring.
- Showers draw a lot: a 10.5 kW electric shower takes 45.6 amps and needs its own circuit, usually 45 A with 10 mm² cable.
- Use the label on the appliance: it gives the power in watts, and often the current in amps.
Tools & materials for this project
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Frequently asked questions
How do you convert watts to amps?
Divide the watts by the volts. 3,000 W ÷ 230 V = 13.0 A. For AC with a power factor below 1, divide by the power factor as well.
How many amps is a 3 kW kettle?
13.0 amps at 230 volts, which is just within a 13 A plug.
How many amps is 2,000 watts?
8.7 amps at 230 volts.
How many amps is a 10.5 kW shower?
45.7 amps at 230 volts, so it needs its own circuit, normally on a 45 A MCB with 10 mm² cable.
What fuse do I need in a plug?
A 3 A fuse for appliances up to about 690 W, 5 A for up to 1,150 W, and 13 A for anything bigger up to 2,990 W. Check the appliance label and manual.
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