Watts to kWh Converter
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What it costs to run
A conversion and sizing aid, not an electrical design. Wiring, breaker and cable choices depend on the cable type, length, installation method and local rules: have a licensed electrician check any new circuit.
kWh = watts × hours ÷ 1,000. 1,500 W for 2 hours is 3 kWh, and a 100 W device left on for a day uses 2.4 kWh. Watts alone cannot be turned into kWh: you need the time.
Watts tell you how fast an appliance uses electricity; kilowatt-hours tell you how much it used, and that is what you pay for. To get from one to the other you need the time it runs. The converter takes the watts and the hours and gives the kWh, then prices them at your state’s average rate or the UK price cap, with the CO₂.
How to convert watts to kWh
Multiply the power in watts by the hours it runs, then divide by 1,000 to turn watt-hours into kilowatt-hours.
kWh = W × h ÷ 1,000. Reverse: W = kWh × 1,000 ÷ h, the average power over that time.
A 60 W fan running 8 hours uses 60 × 8 = 480 Wh, which is 0.48 kWh. A 2,000 W kettle that runs for 3 minutes (0.05 h) uses 2,000 × 0.05 = 100 Wh, or 0.1 kWh: high power, but for so short a time that it costs little.
Watts to kWh chart
Energy for one hour, a full day, and a year at one hour a day, with the cost of one hour at the US average residential price of 18.19¢ per kWh (EIA, January to July 2026).
| Watts | kWh in 1 hour | kWh in 24 hours | kWh a year at 1 h a day | Cost of 1 hour (US average) |
|---|---|---|---|---|
| 5 W | 0.005 | 0.12 | 1.8 | 0¢ |
| 10 W | 0.01 | 0.24 | 3.6 | 0¢ |
| 60 W | 0.06 | 1.44 | 21.9 | 1¢ |
| 100 W | 0.1 | 2.4 | 36.5 | 2¢ |
| 300 W | 0.3 | 7.2 | 109.5 | 5¢ |
| 500 W | 0.5 | 12 | 182.5 | 9¢ |
| 1,000 W | 1 | 24 | 365 | 18¢ |
| 1,500 W | 1.5 | 36 | 547.5 | 27¢ |
| 2,000 W | 2 | 48 | 730 | 36¢ |
| 3,000 W | 3 | 72 | 1,095 | 55¢ |
| 7,200 W | 7.2 | 172.8 | 2,628 | $1.31 |
From kWh to the bill
Multiply the kWh by your price per kWh. The 3 kWh from 1,500 W for 2 hours costs 55¢ at the US average and 79p at the UK price cap of 26.32p per kWh (October to December 2026, which has no VAT on electricity). Prices vary widely by state, from 12.36¢ in North Dakota to 46.28¢ in Hawaii: the converter uses your state’s EIA average, and you can type in your own rate from a bill. A fridge or an air conditioner cycles on and off, so watts × hours overstates it: the electricity cost calculator starts from what one really uses in a year.
The UK figure leaves out the daily standing charge, which you pay whether or not the appliance runs.
Reading the watts on a label
The watts on a label are usually the maximum. A fridge, freezer, heater on a thermostat or an air conditioner switches on and off, so it uses its full watts for only part of each hour; over a day it uses far fewer kWh than watts × 24. For those, the yearly kWh on an ENERGY STAR or EnergyGuide label, or a plug-in energy meter, gives a truer figure. GreenCalculus has worked examples for a refrigerator and a TV.
Common mistakes
- “Watts per hour”. Watts are already a rate. A 100 W bulb uses 100 watt-hours each hour, not “100 watts per hour”.
- Forgetting to divide by 1,000. 1,500 W × 2 h is 3,000 Wh, which is 3 kWh.
- Mixing kW and kWh. An EV charger rated 7.2 kW delivers 7.2 kWh in an hour; a 60 kWh battery is the energy it holds.
- Using the maximum watts for appliances that cycle on and off.
Standards and data sources
| What | Source | Version |
|---|---|---|
| US electricity price | EIA Electric Power Monthly, Table 5.6.B, residential, by state | January to July 2026 |
| UK electricity price | Ofgem energy price cap, Direct Debit unit rate, England, Scotland and Wales | 1 October to 31 December 2026 |
| Grid CO₂e, US | EPA eGRID, state and national location-based factors | eGRID 2023 data |
| Grid CO₂e, UK | DESNZ/DEFRA greenhouse gas conversion factors, UK electricity generation | 2026 |
The conversions are exact physics and need no data. The running cost and CO₂ use figures stored in the GreenCalculus MasterBrain with their source cells, read live by the converter, so they update when the publishers do. The breaker check follows the code text; it is a sizing aid, not a design, and a licensed electrician should check any new circuit.
Frequently asked questions
Multiply the watts by the hours and divide by 1,000. 1,500 W for 2 hours is 1,500 × 2 ÷ 1,000 = 3 kWh.
Exactly 1 kWh. 1,000 W is 1 kW, and 1 kW for 1 hour is 1 kWh.
2.4 kWh (100 × 24 ÷ 1,000).
No. Watts are a rate and kWh an amount; you need how long it runs.
In the US, 18.19¢ on average for homes (EIA, January to July 2026), from 12.36¢ in North Dakota to 46.28¢ in Hawaii. In Great Britain the price cap is 26.32p per kWh from 1 October to 31 December 2026.
About 41.7 W on average (1,000 Wh ÷ 24 h).