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The energy consumed in kilowatt-hours.
A kilowatt-hour is one kilowatt drawn for one hour. A 2 kW heater running for three hours uses 6 kWh. For anything that cycles, such as a fridge or a heat pump, take the figure from a meter reading rather than from nameplate power multiplied by clock hours.
The price of one kWh on your bill.
The unit rate, not the standing charge, and before any separately itemised tax. If your tariff changes by time of day, split the consumption into its bands and run each band at its own rate — one blended figure on a peak and off-peak tariff can be out by a third either way.
Energy consumed
100 kWh
Figures that depend on a rate wait for yours — this page does not assume one.
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kWh to Running Cost Calculator: 100 kWh — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
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How this was calculated
Formula source(s)
- Running cost is the product of energy consumed in kilowatt-hours and the unit rate charged per kilowatt-hour
- Unit rates are set per supplier and per tariff and are not standardised; several markets now vary them by time of day. Take the figure from your own bill.
Inputs used
- Consumption (kWh)
- 100
- Unit rate (per kWh)
What this calculation does not cover
- Non-domestic supplies are not billed on energy alone. A commercial account carries a capacity or demand charge set by the highest sustained kilowatt draw recorded in the billing period, so the same kilowatt-hours pulled quickly cost more than the same energy drawn slowly. No multiplication of consumption by a unit rate can see that, and on a small commercial account the demand element can rival the energy element.
- Energy bought is not heat delivered. A heat pump returns three or four kilowatt-hours of heat for every one taken from the meter, a condensing boiler returns less than the fuel it burns, and a resistance heater returns one for one. Comparing the running cost of two heating options on metered units alone credits the wrong one — divide by each system's seasonal efficiency before the rates are compared.
Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.
Sources checked 2026-09-16 · v1.1.0
Regulatory standards & verification citations2
- Running cost is the product of energy consumed in kilowatt-hours and the unit rate charged per kilowatt-hour
- Unit rates are set per supplier and per tariff and are not standardised; several markets now vary them by time of day. Take the figure from your own bill.
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Most jobs need more than one number. Add the calculators you need next and they open right here, underneath this one — your figures stay on screen and nothing is lost to a page change.
Comparing the running cost of heating options, or justifying an efficiency measure, starts with turning consumption into money. The arithmetic is a single multiplication; the honest difficulty is that there is no universal unit rate — tariffs differ by market, supplier and time of use — so the rate is yours to enter. Two things to keep out of the calculation: standing charges, which are payable whatever you use, and clock hours for anything that cycles, since a fridge or heat pump runs a fraction of the time it is switched on.