Enter a device's wattage and how long it runs to see exactly how many kWh it uses — the unit your utility bill is based on.
Watts measure power at an instant; kWh measure energy used over the time period you entered — multiply the two together (divided by 1000) to go from one to the other.
This is the single calculation underneath almost every electricity bill and every other calculator on this site — watts tell you a device's power draw, hours tell you how long it ran, and multiplying the two (then dividing by 1000 to go from watt-hours to kilowatt-hours) gives you the exact number your utility charges for. See our fuller watts, amps, and volts guide for how this fits with the other basic electrical units.
kWh measures total energy consumed over the billing period, which is what you're actually being charged for — watts alone only describe an instantaneous rate, not a total amount used.
This tool converts watts (power) and hours (time) into kWh (energy) — the kWh to kW calculator instead converts between kWh (energy) and kW (power) when you already have one and a time period, solving a related but distinct conversion.