Quick answer: boiling a kettle costs about 2.9p per litre at 26.32p per kWh. A full 1.7-litre kettle costs about 4.9p, while boiling just one mug’s worth costs under 1p. The amount of water decides the cost, not the kettle’s wattage.
Kettle Cost Per Boil Calculator
Based on how much water you boil. Results update as you type.
How the cost of boiling a kettle is calculated
Heating 1 litre of water by 1°C takes about 0.001163 kWh. From 15°C to 100°C is an 85°C rise, so 1 litre needs about 0.099 kWh in theory. Kettles lose a little heat, so dividing by a typical 90% efficiency gives about 0.11 kWh per litre.
Cost per boil = litres × (100 − start temperature) × 0.001163 ÷ efficiency × price per kWh
For 1 litre: 1 × 85 × 0.001163 ÷ 0.9 = 0.110 kWh, and 0.110 × 26.32p = 2.9p. Day-rate figures use 26.32p per kWh, the Ofgem price cap unit rate for electricity paid by direct debit from 1 October to 31 December 2026. Your own rate is on your bill, so change it in the calculator.
Kettle cost by amount of water
| Water | Energy | Cost per boil | Time at 3kW |
|---|---|---|---|
| 0.25 l (one mug) | 0.027 kWh | 0.72p | 33 s |
| 0.5 l | 0.055 kWh | 1.45p | 1 min 6 s |
| 1 l | 0.110 kWh | 2.89p | 2 min 12 s |
| 1.7 l (full) | 0.187 kWh | 4.91p | 3 min 44 s |
Starting from 15°C at 90% efficiency. Colder winter tap water takes a little more energy and time.
Why boiling only what you need saves money
Boiling 1 litre five times a day costs about £52.76 a year. Boiling half a litre each time, enough for two mugs, halves that to about £26.38. The kettle’s wattage makes no difference to this saving, only the volume of water.
Worked examples
- Tea for one, six times a day: 0.3 litres per boil uses about 0.033 kWh, roughly 0.87p a boil or about 5p a day.
- Always filling the kettle: 1.7 litres, five times a day, costs about 24.6p a day, roughly £90 a year.
Frequently asked questions
How much does it cost to boil a kettle?
It depends on how much water you boil. At 26.32p per kWh, boiling 1 litre from 15°C costs about 2.9p, a full 1.7 litres about 4.9p, and a single mug (0.25 litres) about 0.7p.
Does a 3kW kettle cost more than a 2kW kettle?
Not per boil. Both need the same energy to bring the same water to the boil; the 3kW kettle just does it faster. The amount of water is what changes the cost.
Is it cheaper to boil water in a kettle or on a gas hob?
Gas is cheaper per kWh, but a hob loses much more heat around the pan, while a kettle puts most of its energy into the water. For small amounts, an electric kettle is quick and wastes little.
How can I make boiling the kettle cheaper?
Boil only the water you need, keep the kettle descaled, and pour extra hot water into a flask instead of reboiling it later.