What it costs to use an electric kettle

The kettle is one of the most powerful appliances in the kitchen, often 2,000-3,000 W, but it only runs for a few minutes. Its energy use depends almost entirely on one thing: how much water you heat. This calculator uses the physics of water to estimate the cost of each boil and per year, and shows how much you spend on water you boil without using.

It works in any currency: enter the energy price from your bill.

How the calculation works

• Energy: heating one litre of water by one degree takes 4.186 kJ. Multiply by the litres and the temperature rise and divide by 3,600 to get kWh.
• Efficiency: some heat warms the kettle and the air; electric kettles are generally very efficient, often around 80-90%.
• Cost: kWh per boil × boils per day × 365 × energy price.
• Time: the energy divided by the kettle's power.
• Excess: the part of the boiled water you do not use, as a percentage of the water boiled.

What each litre costs

Water from 15 to 100 °C, 85% efficiency, a 2,200 W kettle, four boils a day, energy at 0.30 per kWh:

Each boil costs a few cents, but the cost is proportional to the litres: a full 1.7-litre kettle costs almost seven times a single mug.

The real waste: water you do not use

If you need a single 0.25-litre mug, four times a day:

Filling the kettle to the top for one mug costs about seven times what you need. Fill only what you need, above the minimum mark: it is the easiest saving, and the quickest too, because less water boils sooner.

You do not always need to boil

One litre of water, same data:

Many drinks, such as green tea, are better made with water below 100 °C. A kettle with temperature control saves a little energy and time.

The reading bands

• No excess: you boil only the water you use.
• Up to 25%: a small excess, often due to the kettle's minimum.
• 25% to 50%: a large part of the boiled water goes unused.
• Above 50%: more than half the boiled water is wasted.

Limits of the calculator

The calculation treats a litre of water as one kilogram and assumes constant efficiency. It does not include standby use or limescale, which slows heating over time: descaling the kettle helps. Tap water temperature changes with the seasons.

Frequently asked questions

How much energy does an electric kettle use?

Bringing 1 litre from 15 to 100 °C takes about 0.12 kWh at 85% efficiency. At four boils a day that is about 170 kWh a year.

How much does it cost to boil a kettle?

With energy at 0.30 per kWh, about 0.035 for one litre and about 0.009 for a single mug.

Does a kettle use a lot because it is so powerful?

No: high power makes it boil faster, but the energy needed depends on the litres and the temperature rise.

How much do you save by filling only what you need?

A lot, in proportion: for one mug, a full kettle costs about seven times more.

How long does a kettle take to boil?

With a 2,200 W kettle, about 3 minutes for a litre and under a minute for a mug.

Is a kettle cheaper than the hob?

An electric kettle is usually more efficient than a pan on the hob, because the heat goes straight into the water; the cost also depends on the gas or electricity price.

Does limescale increase energy use?

Yes, a little: a layer of limescale slows heat transfer. Descaling the kettle regularly helps.

Why enter the starting water temperature?

Because the energy depends on the temperature rise: in winter tap water is colder and needs more energy.

Does it work in any currency?

Yes. Enter the price per kWh in your currency; kWh do not depend on the currency.