What is a kWh?
A kWh, or kilowatt-hour, is a unit of energy. It is the number used on electricity bills and EV charging prices.
A kWh is a kilowatt-hour: a measure of energy used over time. If something uses 1 kilowatt of power for 1 hour, it has used 1 kWh of energy.
For drivers, kWh matters because electric car charging is priced by the kilowatt-hour. For households, it matters because electricity bills show how many kWh you used and the pence-per-kWh rate you paid.
Why kWh matters
kWh is the bridge between electricity use and cost. A charger, appliance or car may use power at a certain rate, but your bill is based on total energy used. That is why the same EV can cost very different amounts to charge depending on the price per kWh.
In simple terms, a lower kWh price usually means cheaper charging, while a less efficient car needs more kWh to cover the same mileage.
Estimate your charging cost
Use battery size, charge level, price per kWh and charging loss to estimate EV charging cost.
How kWh works
A kilowatt is a rate of power. A kilowatt-hour is the amount of energy used when that power is used for time. That distinction matters because appliances and chargers may be described in kilowatts, but the bill is charged in kilowatt-hours.
Energy used = power × time
1kW used for 1 hour = 1kWh
2kW used for 3 hours = 6kWhFor EV charging, the battery size is often shown in kWh. A 60kWh battery can store about 60kWh of energy when full, although charging losses mean the wall charger may draw slightly more than the battery receives.
kWh and EV charging
Electric car charging cost is usually worked out by multiplying the kWh used by the price per kWh. If you charge at home, this price normally comes from your electricity tariff. If you charge publicly, it comes from the public charging network.
EV charge cost = kWh used × price per kWh
Cost per mile = charge cost ÷ miles addedA 40kWh charge at 26.11p/kWh would cost about £10.44 before any standing charge, tariff difference or charging loss adjustment. The same 40kWh at a 9p overnight rate would cost £3.60.
kWh and energy bills
Your electricity bill is built from two main parts: the unit rate and the standing charge. The unit rate is the price you pay for each kWh you use. The standing charge is a daily fixed cost that applies even if you use little energy.
| Bill item | What it means | Why it matters |
|---|---|---|
| kWh used | The amount of electricity consumed. | More kWh means a higher usage cost. |
| Unit rate | The pence-per-kWh price. | Controls how expensive each unit is. |
| Standing charge | A daily fixed charge. | Can make bills higher even with low usage. |
| Time-of-use rate | Different prices at different times. | Can make overnight EV charging cheaper. |
Current UK context
For 1 July to 30 September 2026, Ofgem's published price-cap information shows an average Direct Debit electricity unit rate of 26.11p per kWh. This is a useful benchmark, but it is not the same as every household's exact rate because region, meter type, payment method and tariff can change the price.
For company-car context, GOV.UK's advisory electric rates from 1 June 2026 are 7p per mile for home charging and 15p per mile for public charging. Those are advisory mileage rates, not a replacement for using your own pence-per-kWh price in a calculator.
Worked example
Suppose an electric car adds 35kWh to its battery and your electricity rate is 26.11p per kWh.
35 × £0.2611 = £9.1385
Rounded charging cost = £9.14If that charge adds 120 miles, the energy-only cost is about 7.62p per mile. Public charging or a different tariff could change that result materially.
Common mistakes
FAQs
Is kWh the same as kW?
No. kW measures power, while kWh measures energy used over time. A 7kW charger running for one hour would use about 7kWh before losses and charging behaviour are considered.
How many kWh does an EV use per mile?
It depends on the car and conditions. Many calculators ask for miles per kWh because it is easier to estimate how far the car travels for each unit of energy.
Why does public charging cost more per kWh?
Public charging prices include network costs, equipment, location costs and often faster charging convenience. The price per kWh can be much higher than home charging.
Should I use the Ofgem price cap rate for EV charging?
Use it only as a rough benchmark. Your actual tariff, off-peak EV rate or public charging network price is more accurate for a real calculation.