Quick answer: Boiling 1 litre of water takes about 0.11 kWh, roughly 2.9p under the Ofgem price cap of 26.32p per kWh. A single cup costs about 0.7p, and a full 1.7-litre kettle about 4.9p.
Kettle power (usually 2.2 to 3 kW) only changes how fast it boils, not how much energy it takes. What you pay for is the water you heat.
Cost per boil
| Amount | Energy | UK cost |
|---|---|---|
| One mug, about 250 ml | 0.03 kWh | 0.7p |
| Half a kettle, 1 litre | 0.11 kWh | 2.9p |
| Full kettle, 1.7 litres | 0.19 kWh | 4.9p |
| Five 1-litre boils a day for a year | 201 kWh | £52.84 |
How we worked it out
Heating 1 litre of water by 85°C takes 4.186 kJ per °C, about 356 kJ, or 0.099 kWh. Allowing for about 10% heat lost to the kettle and the air gives roughly 0.11 kWh. A 3 kW kettle delivers that in about 2 minutes 15 seconds.
How to boil for less
- Boil only the water you need. Filling the kettle for one mug wastes most of the energy.
- Descale it. Limescale on the element slows heating.
- Use a flask for repeated hot drinks instead of reboiling.
- Use the kettle for pasta water before it goes on the hob: a kettle heats water more efficiently than most hobs.
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Frequently asked questions
Is a 3 kW kettle more expensive than a 2 kW kettle?
No. It draws more power but boils faster, so the energy per litre is about the same.
How much does a kettle cost to run per year?
Five 1-litre boils a day add up to about 200 kWh a year: roughly £52.84 under the price cap.
A real example: tea drinkers
A household that boils the kettle six times a day, about 400 ml each time, uses roughly 96 kWh a year, around £25.36 under the current price cap. If the same household filled the kettle to 1.5 litres every time, it would use nearly four times as much, around £95.11 a year.
Boiling only the water you need is the simplest saving in the kitchen. Most kettles have a cup scale on the side.
Kettle, hob or microwave?
An electric kettle is the most efficient way to boil water at home, because the element is in direct contact with the water and it switches off as soon as it boils. Boiling water in a pan on an electric hob loses heat to the air, and microwaves are less efficient for boiling larger amounts. For hot water through the day, an insulated flask filled once can save repeated boiling.
More questions readers ask
Does limescale make a kettle cost more?
A thick layer of limescale slightly slows heating and makes the kettle work longer. Descale it regularly with a kettle descaler or citric acid in hard water areas.
Are instant hot water taps cheaper?
They avoid overfilling, but many keep a small tank hot all the time, which uses standby energy. For most households a kettle used carefully is cheaper.
Sources
- Ofgem, Energy price cap.
- Our methodology.