Free household bill check
Appliance electricity cost calculator
Turn watts or kW into kWh and pounds for your chosen hours and days. Check a fan heater, lamp or another electrical load using your own tariff.
Reviewed 19 October 2026 · BillDecoded editorial team · Methods and limitations
Calculate a heater or appliance's electricity use
Use the appliance's electrical input power at the setting you plan to use. These are arithmetic estimates, not measured product tests. Inputs stay in your browser.
Examples you can reproduce
BillDecoded's own calculations at 26.32p/kWh, using the assumptions shown. These are not average measured consumption figures for named products.
| Illustrative load | Use assumption | Energy | Usage cost |
|---|---|---|---|
| 2 kW heater | 1 hour, continuous | 2 kWh | £0.53 |
| 2 kW heater | 3 hours/day × 30 days, continuous | 180 kWh | £47.38 |
| 2 kW heater | Same hours, assumed 50% active share | 90 kWh | £23.69 |
| 10 W lamp | 6 hours/day × 30 days, continuous | 1.8 kWh | £0.47 |
| 100 W television example | 4 hours/day × 30 days, continuous | 12 kWh | £3.16 |
In the 2 kW example, 180 × 26.32 ÷ 100 = £47.376 before currency rounding. A 50% share is an explicit scenario, not a promise that a heater will use half its rated power.
Watts, kW, kWh and pounds
Watts and kilowatts describe power. Kilowatt-hours describe energy used over time. A device labelled 2,000 W is not using 2,000 kWh each hour: divide by 1,000 to get 2 kW, then multiply by operating hours.
Enter electrical input power, not microwave cooking-output power, a heat pump's heat output or a motor's mechanical output. For appliances that change power frequently, an energy-label figure or measured kWh is more useful than assuming the nameplate maximum runs all day.
Already have measured kWh? Use the kWh to cost calculator. Compare two dated meter readings with the reading-to-bill calculator. Use the Economy 7 comparison for day/night use instead of mixing rates here.
Check whether this could explain a bill increase
- Use the same number of days as the bill comparison.
- Estimate additional appliance use, not hours that were already included in the old bill.
- Multiply the added kWh by the tariff for that period.
- Check actual versus estimated meter readings, tariff changes and account adjustments separately.
The output is an extra usage charge. Adding the household standing charge to every appliance would count it repeatedly. Use the standing-charge calculator once for the supply period when estimating a whole bill.
Why an electricity bill can be high · Check a disputed meter reading · Review a monthly payment.
Source, tariff dates and limits
The reference price is from Ofgem's dated unit-rate table. GB regions, tariffs and payment methods differ. Enter your own tax-inclusive rate, including outside GB. The current-reference button refuses to label an expired reference as current.
The calculator models a single non-negative unit rate for up to 366 days. It does not forecast future rate changes, model solar self-consumption, storage losses, appliance safety, room heat demand or time-of-use billing. Currency is rounded for display. Read the calculation method. Independent information and arithmetic only.
Frequently asked questions
How much does a 2 kW heater cost per hour?
At the dated October–December 2026 GB example price of 26.32p/kWh, one continuous hour uses 2 kWh and costs 52.64p, before standing charges.
Does a 2 kW appliance always use 2 kWh each hour?
Only when it draws 2 kW continuously for the whole hour. Cycling or changing settings can change actual energy use.
Should I add a standing charge to every appliance?
No. It is a separate daily supply charge. The tool estimates appliance usage cost so it is not counted repeatedly.
Can this prove what caused my high bill?
No. Compare the same period, actual meter readings, additional usage and the applicable tariff. These are transparent assumptions, not measurements of your home.