Advanced options
What The Kettle Cost Calculator Works Out
- Per boil: litres boiled x about 0.11 kWh per litre (the energy to take water from tap-cold to boiling) x the electricity rate, which defaults to the current Ofgem price cap unit rate (26.32p per kWh from October 2026). A litre costs about 3p at that rate. Water's specific heat capacity fixes the energy per litre, so the 3kW rating on the box buys speed, not economy.
- Per day and per year: the per-boil cost x boils a day, then x 365. A five-boil tea habit of a litre a time runs about 15p a day and GBP 53 a year, mid-table among kitchen appliances and a rounding error beside heating.
- The fill line: a full 1.7 litre kettle boiled for a single mug spends nearly six times the energy the mug needed, so "boil what you use" is the entire genre of kettle advice. The yearly card shows what filling it every time would cost.
- Own fill and energy per litre (advanced): enter a measured fill and adjust the kWh per litre (0.11 from a 10 degree tap; a little less in summer, more with very cold winter mains).
- Limescale penalty (advanced): fur insulates the element and lengthens boils, adding a few percent to the energy. Descaling with cheap citric acid restores it; the card shows the kilowatt-hours a descale would recover.
- Per cup and per person (advanced): the boil cost split by cups made per boil, and the annual cost split between the people sharing the kettle.
- Gas hob comparison (advanced): the same boil in a pan on a gas hob, which loses most of its heat around the pan (around 40% efficient). Gas-hob boiling usually costs slightly less per boil at gas prices; induction and kettle roughly tie.
- Flask saving (advanced): the thriftiest boil of all is the flask: one boil poured all afternoon, the allotment-shed optimisation that beats every gadget. Enter the boils a day it would replace.
- Electricity used per year (advanced): annual kilowatt-hours against a typical household's 2,700 kWh. Trivial per home and mighty in aggregate: the National Grid braces for the TV pickup as a nation boils in unison at soap-opera credits, and Dinorwig's pumped storage spins up for it.