How much does it cost to boil a kettle?
Boiling one litre of cold tap water takes about 0.11 kWh, which costs about 2.9p at the Ofgem cap rate of 26.32p/kWh. A single mug (about 250 ml) costs under a penny: about 0.7p. A completely full 1.7-litre kettle costs about 4.9p.
The kettle's wattage barely matters. A 3kW kettle boils faster than a 2.2kW one, but the water still needs about the same energy.
Prices last checked: 26 September 2026 · Source: Ofgem energy price cap, 1 October to 31 December 2026 · Great Britain average, standard variable tariff, paid by Direct Debit
Cost per boil by amount of water
The figures are worked out from the energy needed to heat water from about 15°C to boiling, assuming about 90% of the electricity ends up in the water (some heat is lost to the kettle body and the air). That is an assumption, and you can change it in the calculator.
| Water boiled | Energy | Cost per boil | 5 boils a day, per year |
|---|---|---|---|
| One mug (250 ml) | 0.027 kWh | 0.7p | £13.19 |
| Two mugs (500 ml) | 0.055 kWh | 1.4p | £26.37 |
| One litre | 0.11 kWh | 2.9p | £52.75 |
| Full kettle (1.7 litres) | 0.187 kWh | 4.9p | £89.67 |
The real saving: boil only what you need
Filling the kettle to the top for one mug is the most common kettle "waste". The extra water is heated to boiling and left to cool. Boiling 1.7 litres instead of 250 ml costs about 4.2p extra each time. Five times a day, that is about £76.49 a year, for water you never drink.
That is not a huge sum on its own, but it is the one kettle habit that makes a visible difference. Many kettles have a cup-level marker. The minimum fill line is there to protect the element, so don't go below it.
Kettle vs other ways to heat water
- Kettle vs pan on an electric hob. The kettle wins. Its element sits in the water, while a pan loses heat from its sides and the hob around it.
- Kettle vs pan on a gas hob. Gas is cheaper per kWh (7.97p at the cap against 26.32p), but a gas flame loses a lot of heat around the pan. For small amounts the difference is pennies either way. The kettle is quicker.
- Kettle vs microwave for one mug. Similar energy for small volumes. The kettle is usually faster and more even.
- Instant boiling-water taps. These keep a tank hot all day, so they have a standing heat loss that a kettle doesn't. Whether they cost more depends on the model's standby use, which the manufacturer should list.
Common mistakes
- Thinking a lower-wattage kettle is cheaper. It takes longer to deliver the same energy. The cost per boil is almost identical.
- Reboiling water that has cooled. Each reboil pays again for most of the heat.
- Ignoring limescale. In hard-water areas scale builds up on the element. Descaling keeps the kettle working as it should.
Limits of this estimate
The 90% figure for heat reaching the water is an assumption, not a measurement. Tap water temperature varies by season and region. Costs use the Ofgem cap average unit rate for Great Britain, Direct Debit.
Frequently asked questions
How much does it cost to boil a full kettle?
About 4.9p for 1.7 litres of cold tap water at the cap rate.
How much does a cup of tea cost in electricity?
Boiling enough for one mug costs about 0.7p, if you only boil that much.
Is it cheaper to boil a kettle or use a hot water tap?
For occasional use, the kettle, because it doesn't keep water hot between uses. For a busy household the gap narrows. Check the tap's standby consumption.