Boiling a full 1.7 litre kettle costs about 5p. A single mug of water costs under a penny. Both figures are at the Ofgem price cap rate of 26.32p per kWh, which applies from 1 October to 31 December 2026.
That is the answer. The more useful question is what it adds up to over a year, and that depends almost entirely on how much water you put in.
How the sum works
You only need one piece of arithmetic. Electricity is billed per kilowatt hour, and a kettle's wattage tells you how fast it draws power:
kWh used = kilowatts × hours running
A 2200W kettle is 2.2kW. Run it for three minutes, which is 0.05 of an hour, and it uses 2.2 × 0.05 = 0.11 kWh. At 26.32p, that boil cost just under 3p.
Working from the water instead of the clock gives the same answer and is more reliable, because it does not depend on how cold your tap runs. Heating a litre of water from cold to boiling takes roughly 0.11 kWh once you allow for the heat a kettle loses to its own body and to steam.
What each fill level costs
| Water in the kettle | Energy used | At 20p/kWh | At 26.32p/kWh | At 30p/kWh |
|---|---|---|---|---|
| One mug, 250ml | 0.03 kWh | 0.5p | 0.7p | 0.8p |
| Minimum fill, 0.8L | 0.09 kWh | 1.8p | 2.3p | 2.6p |
| Two thirds, 1.2L | 0.13 kWh | 2.6p | 3.5p | 3.9p |
| Full, 1.7L | 0.19 kWh | 3.7p | 4.9p | 5.6p |
Find your own unit rate on your latest bill or in your energy app, then multiply it by the kWh column. The standing charge does not come into it: that is a fixed daily fee you pay whether you boil anything or not.
The minimum fill nobody mentions
Every cost guide tells you to boil only what you need. Almost none mention that your kettle will not let you.
Kettles have a minimum fill line, usually somewhere between 0.5 and 1 litre, and it exists for a good reason: below it, the element is not properly covered and will overheat. On most 1.7 litre kettles the minimum is around 0.8 litres, which is roughly three mugs.
So the theoretical "under a penny for one mug" is not actually available to you. Your real floor is about 2p a boil, and the genuine saving is in not going past the line you need.
What it adds up to over a year
Take a household making six hot drinks a day, which is unremarkable in Britain.
- Filling to the minimum line each time: 2.3p × 6 × 365 = about £50 a year
- Filling to the top each time: 4.9p × 6 × 365 = about £107 a year
The gap is roughly £57 a year for doing nothing more than watching the water level. That is the entire energy-saving story of a kettle in one line, and it is worth more than any efficiency feature on any box.
This is why a clear water window matters more than the wattage. If you cannot see the level while you fill, you will overfill, because everyone does.
Does a higher wattage kettle cost more to run?
No, and this catches people out constantly. A 3000W kettle draws more power than a 2200W one, but it finishes sooner, so the total energy is much the same. Watts multiplied by a shorter time gives a similar number of kilowatt hours.
If anything the faster kettle is marginally cheaper, because a shorter boil loses less heat to the kettle body and the air. We went through that properly in wattage explained.
Does limescale cost you money?
Yes, though less than the internet suggests. Limescale is a poor conductor, so a coated element has to run longer to deliver the same heat into the water. On a badly scaled kettle that is a real but small penalty, nothing like the overfilling number above.
The stronger argument for descaling is that scale shortens the life of the kettle and puts flakes in your tea. If yours is due, here is how to descale a kettle.
Five things that actually reduce the cost
- Fill to the line you need, not the top. Worth about £57 a year on the numbers above. Everything else on this list is rounding error by comparison.
- Do not reboil out of habit. Water that has cooled from boiling to 80°C needs only a fraction of the energy to get back, but pressing the switch again heats it from wherever it actually is, and most of us press it having forgotten entirely.
- Descale it. Small gain, but free.
- Use the kettle rather than the hob. An electric kettle puts nearly all its heat into the water. A pan on a gas ring sends most of it up the sides.
- Ignore "eco" marketing. There is no meaningful efficiency difference between mainstream kettles. The water level is the variable.
Common questions
How much does it cost to boil a kettle for one cup?
Under a penny in theory, about 2p in practice, because most kettles have a minimum fill of around 0.8 litres and will not safely boil less.
How many watts is a kettle?
UK kettles run between about 1800W and 3000W, with 2200W to 3000W being the common range. The ceiling is set by the 13A plug, which cannot safely carry much more.
Is it cheaper to boil water in a microwave?
No. A kettle is the more efficient appliance for heating water, and it is faster.
Does the standing charge affect the cost of a boil?
No. The standing charge is a fixed daily fee, currently 54.83p a day, charged whether or not you use any electricity.
How much electricity does a kettle use per year?
At six boils a day, somewhere between 190 and 400 kWh depending on how full you fill it. That is roughly £50 to £107 at the current cap.
The short version
About 5p for a full kettle, about 2p if you fill to the minimum, and the difference between those two habits is around £57 a year. Wattage barely matters. Limescale barely matters. The water level is the whole game, which is why the Toastley 1.7L kettle puts a clear window down the side of the body where you can actually see it while you pour.
Rates used: Ofgem energy price cap for direct debit customers, 26.32p per kWh and 54.83p daily standing charge, applying from 1 October to 31 December 2026. Check the current figure on the Ofgem price cap page, and use your own unit rate with the table above.