How we calculate
Every cost on Pence Per Hour comes from the same two-line sum, and we show it on each page so you can check us.
The formula
Energy used (kWh) = watts ÷ 1,000 × hours
Cost = kWh × unit rate (pence per kWh)
Example: a 2,000 W heater for 3 hours uses 2,000 ÷ 1,000 × 3 = 6 kWh. At 26.32p per kWh, that costs 6 × 26.32 = £1.58.
The unit rate we use
Our default is the Ofgem energy price cap for the current quarter. From 1 October to 31 December 2026, it's 26.32p per kWh for electricity, with a standing charge of 54.83p a day. These are GB averages for Direct Debit customers, and there's no VAT on electricity from 1 October 2026 to 31 March 2027 (Ofgem). We update the defaults and "last updated" dates each time Ofgem resets the cap, every three months.
We leave the standing charge out of appliance costs, because you pay it whether or not the appliance is on. Every calculator lets you type in your own rate.
Where wattages come from
We label every figure so you know what kind of number it is:
| Label | What it means | Used on this site? |
|---|---|---|
| Typical (published) | A rating range or figure published by a named source, such as a charity, consumer body or manufacturer, and cross-checked against a second source wherever one exists | Yes, for all figures in this version |
| Energy label | The kWh figure from an appliance's official energy label, taken from the manufacturer's published label (the same labels are registered in the EU EPREL database) | Yes, for example models in our fridge-freezer, washing machine and TV guides |
| Measured | Measured by us with a plug-in energy monitor, with the date and model stated | Not yet. We'll only use this label for things we've actually measured. |
For an electric car, the cost depends on the car's efficiency (kWh per 100 miles) rather than a wattage. Our EV calculator uses Which?'s lab-tested efficiency figures, adds an editable allowance for charging losses (10% by default), and prices the electricity at the cap rate or an overnight tariff you enter.
For appliances without an energy label, such as kettles, heaters and dehumidifiers, we use rated wattages cross-checked across sources such as Energy Savers, National Energy Action, the Centre for Sustainable Energy, Which? test results and manufacturers' specification sheets. We show a range rather than a single number. The "typical" value is the midpoint of the published range, unless a source states a typical figure itself, in which case we use that and say so.
Appliances that switch on and off
A rated wattage is a maximum. Fridges, ovens, heaters with thermostats, tumble dryers, washing machines and dehumidifiers with humidistats only draw full power part of the time. Where we can, we use energy-per-cycle or energy-per-load figures instead, such as Which?'s measured tumble dryer costs. Where we give an "on X% of the time" figure, we label it as an illustration.
Rounding
We show costs under £1 to one decimal place of a penny, and larger amounts to the nearest penny. A month is a year ÷ 12, and a year is 52 weeks.
Spotted an error?
Please tell us through the contact page. We'll check it against the source and correct the page, with a new "last updated" date. See our editorial policy.