How much does it cost to boil a kettle?
Boiling 1 liter of water takes about 0.1 kWh: roughly 3p under the UK price cap, 2¢ at the US average price. The physics, a full-kettle example and how to cut the cost.
- Heating 1 liter of water from 15 °C to 100 °C needs about 0.099 kWh in theory; allowing for some heat loss, about 0.11 kWh in practice (our assumption: 90% efficiency).
- That is roughly 2.9p per liter at the UK price cap (26.32p/kWh) and about 2¢ per liter at the US average (18.31¢/kWh).
- A full 1.7 L kettle costs about 5p in the UK.
- Measured in real homes, kettles used 32 kWh a year at the median: about £8 a year at UK prices.
The physics in one line
Heating water takes a fixed amount of energy: about 4.19 kJ per kilogram per degree Celsius (water’s specific heat capacity). One liter of water weighs about 1 kg, so bringing it from tap temperature (say 15 °C) to boiling (100 °C) takes:
1 kg × 4.19 kJ/kg·°C × 85 °C ≈ 356 kJ ≈ 0.099 kWh
That is the theoretical minimum. A real kettle also warms its own body and loses some heat to the air. We assume a 90% efficiency in the figures below, which gives about 0.11 kWh per liter. Your kettle may do slightly better or worse; a plug-in energy monitor will tell you.
Interestingly, the kettle’s wattage barely matters for cost: a 3 kW kettle boils faster than a 2 kW one, but the energy needed to heat the water is the same.
Cost per boil
| Amount of water | Energy (approx.) | UK (26.32p/kWh) | US (18.31¢/kWh) | France (€0.2001/kWh) |
|---|---|---|---|---|
| 1 cup (250 ml) | 0.027 kWh | 0.7p | 0.5¢ | €0.005 |
| 1 liter | 0.11 kWh | 2.9p | 2.0¢ | €0.022 |
| Full kettle (1.7 L) | 0.19 kWh | 4.9p | 3.4¢ | €0.037 |
Prices: Ofgem price cap, Direct Debit average, 1 Oct–31 Dec 2026; EIA US residential average, July 2026; EDF regulated Base tariff from 1 Aug 2026.
Per year
In ADEME’s measurements of 38 kettles in French homes (July 2023 – July 2024), the median kettle used 32 kWh a year (middle half 16–54 kWh). At UK prices that is about £8.40 a year; at the US average, about $5.90. British households, who boil more water for tea, may use more.
How to cut the cost
- Boil only what you need. This is the single biggest saving: boiling a full kettle for one cup uses about seven times the energy actually needed for that cup.
- Use the minimum-fill line, but don’t go below it, for safety and to protect the element.
- Descale regularly in hard-water areas: limescale on the element slows heating.
- Don’t reboil water that has just boiled and is still hot.
A kettle is usually more efficient than heating water in a pan on an electric hob, because the element sits directly in the water. A microwave can be efficient for a single cup, but the difference is a fraction of a penny.
Context: the kettle in your bill
Compared with a fridge-freezer (268 kWh a year at the median) or an electric water heater (1,179 kWh), the kettle is a small item. Its cost per use is tiny; it only adds up because of how often it is used. See all appliances in our measured appliance energy data.