How this calculator works
Watts are volts times amps. For loads with a power factor of 1 that is the whole sum. With a lower power factor, the watts doing work are the volt-amps times the power factor. For three-phase, multiply by 1.732 and use the line voltage.
Worked example: a 13 A plug on 230 V can supply 2,990 W, which is 2.99 kW. 3 A is 690 W, 16 A is 3,680 W, a 32 A ring main is 7,360 W and a 40 A circuit is 9,200 W. A three-phase 32 A supply at 400 V and a power factor of 0.9 is 20.0 kW.
Amps to watts on 230 V mains
Power factor 1.
| Amps | Watts | Typical use |
|---|---|---|
| 3 A | 690 W | Plug fuse for lamps and chargers |
| 5 A | 1,150 W | Plug fuse for small appliances |
| 10 A | 2,300 W | Lighting circuit (6 A is typical) |
| 13 A | 2,990 W | A 13 A plug |
| 16 A | 3,680 W | Immersion heater or radial circuit |
| 20 A | 4,600 W | Radial socket circuit |
| 32 A | 7,360 W | Ring main or cooker |
| 40 A | 9,200 W | Electric shower, cooker |
| 45 A | 10,350 W | Large shower, cooker |
| 63 A | 14,490 W | Consumer unit feeder |
Tips before you buy
- A 13 A plug carries up to 2,990 W at 230 V, which is why kettles and heaters are limited to 3 kW.
- A ring main protected by a 32 A MCB can carry 7,360 W in total, but any one plug is limited to 13 A.
- Mains voltage in the UK is 230 V (+10%, −6%), so the real power of a heater is within a few percent of this.
- Motors and electronics have a power factor below 1, so the power doing work is less than volts times amps.
- To work out running cost, multiply the kilowatts by the hours and by your price per kWh.
Tools & materials for this project
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Frequently asked questions
How many watts is a 13 amp plug?
2,990 watts at 230 volts. That is why most plug-in heaters and kettles are limited to 3 kW.
How many watts is 16 amps?
3,680 watts (3.68 kW) at 230 volts.
How many watts can a 32 amp ring main take?
7,360 watts (7.36 kW) in total, shared by all the sockets, though any single plug is limited to 13 A.
How many watts is a 40 amp circuit?
9,200 watts (9.20 kW), as for a large shower or cooker.
How many watts is 3 amps?
690 watts at 230 volts: the limit for a 3 A plug fuse.
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