Watts to kWh calculator
Power tells you how fast energy is being used. Time turns that power into energy.
Watts and kWh are not the same thing
A watt is a unit of power. A kilowatt-hour is a unit of energy. Electricity meters and bills usually track energy because it captures both how much power a device draws and how long it runs.
Common conversions
| Power | Time | Energy |
|---|---|---|
| 100 W | 10 h | 1 kWh |
| 500 W | 2 h | 1 kWh |
| 2,000 W | 30 min | 1 kWh |
New to the difference between power and energy? Our guide Watts vs kWh explained covers the concept with everyday examples. This page is the quick converter and reference table.
Watts to kWh conversion table
kWh for common wattages over typical running times, with the cost of one hour at the UK Ofgem price cap unit rate (26.32p/kWh, 1 October to 31 December 2026).
| Power | 1 hour | 8 hours | 24 hours | Cost of 1 hour (UK) |
|---|---|---|---|---|
| 5 W (phone charger, LED night light) | 0.005 kWh | 0.04 kWh | 0.12 kWh | 0.1p |
| 10 W (LED bulb, router) | 0.01 kWh | 0.08 kWh | 0.24 kWh | 0.3p |
| 60 W (laptop) | 0.06 kWh | 0.48 kWh | 1.44 kWh | 1.6p |
| 100 W (TV) | 0.1 kWh | 0.8 kWh | 2.4 kWh | 2.6p |
| 500 W | 0.5 kWh | 4 kWh | 12 kWh | 13p |
| 1,000 W (1 kW) | 1 kWh | 8 kWh | 24 kWh | 26p |
| 1,500 W (air fryer) | 1.5 kWh | 12 kWh | 36 kWh | 39p |
| 2,000 W (2kW heater) | 2 kWh | 16 kWh | 48 kWh | 53p |
| 3,000 W (kettle, immersion heater) | 3 kWh | 24 kWh | 72 kWh | 79p |
| 7,400 W (7kW EV charger) | 7.4 kWh | 59.2 kWh | 177.6 kWh | £1.95 |
kWh back to watts
To go the other way you need a time period: average watts = kWh ÷ hours × 1,000. A plug-in monitor that shows 1.2 kWh after 3 hours means the appliance averaged 400 W. That is also how to work out a fridge's real average draw from its energy label: 250 kWh a year ÷ 8,760 hours × 1,000 ≈ 29 W.
To turn kWh into money, multiply by your unit rate, or use the electricity cost calculator. UK readers can find the current rate on the UK price per kWh page.
Why the difference between watts and kWh confuses so many bills
Almost every appliance sold in Europe carries a wattage rating, yet almost every electricity bill charges in kilowatt-hours — and that mismatch is the single most common source of confusion when people try to estimate running costs. Power (watts) describes the rate energy is being consumed at a given instant, similar to speed. Energy (kilowatt-hours) describes the total amount consumed over a period, similar to distance travelled. A car travelling at 100 km/h for half an hour covers the same distance as one travelling at 50 km/h for a full hour; in the same way, a 2,000 W appliance run for 30 minutes uses exactly as much energy as a 1,000 W appliance run for a full hour — both equal 1 kWh. Understanding this relationship is the foundation for every other calculator on this site, because every running-cost estimate is really just this conversion followed by a multiplication against your unit price.
Where the confusion usually shows up
Retail listings, appliance labels and forum posts often quote wattage without any indication of how long a device typically runs, which makes it tempting — but wrong — to compare two appliances by wattage alone. A 3,000 W kettle boiling water for four minutes uses far less energy than a 100 W lamp left on for eight hours, even though the kettle looks far more powerful on paper. Converting both to kWh removes the guesswork and gives you a genuinely comparable number.
More worked conversions
| Power | Time | Energy |
|---|---|---|
| 60 W | 16 h 40 min | 1 kWh |
| 150 W | 6 h 40 min | 1 kWh |
| 1,200 W | 50 min | 1 kWh |
| 3,000 W (kettle) | 20 min | 1 kWh |
Frequently asked questions
What does kWh actually stand for?
Kilowatt-hour — the amount of energy used by a 1,000 W (1 kW) load running for one hour. It is the standard billing unit for electricity across Europe.
Is 1,000 Wh the same as 1 kWh?
Yes. A kilowatt-hour is exactly 1,000 watt-hours; the two units describe the same amount of energy, just at different scales.
How do I convert kWh back into watts?
You need a time period as well. Divide kWh by hours and multiply by 1,000 to get the average watts a device drew over that period.
Why do smart meters show kW, not kWh, in real time?
A smart meter's live display usually shows instantaneous power draw (kW), which is why it fluctuates as appliances switch on and off. Your bill totals that draw over time into kWh.
Does this conversion change with different currencies or countries?
No. Watts, hours and kWh are physical units that do not depend on currency or location — only the price you pay per kWh varies by country and supplier.