Most people land here holding two numbers that will not talk to each other. A spec sheet or an appliance label gives watts. An electricity bill gives kilowatt-hours. They are not the same kind of measurement, and no amount of staring converts one into the other.
A kilowatt is a rate: how fast something draws power right now. A kilowatt-hour is a quantity: that rate multiplied by how long it ran. The missing piece between them is always time, which is why the converter above asks for a duration in both directions and cannot work without one.
No rates, no dollars, nothing uploaded. This page converts units and stops.
Watts or kilowatts to kilowatt-hours:
kWh = kW x hours
kWh = (watts / 1,000) x hours
Kilowatt-hours back to average kilowatts:
average kW = kWh / hours
That is the entire arithmetic. The only thing to be careful about is the 1,000: a kilowatt is 1,000 watts, so a wattage off a label has to be divided by 1,000 before it is multiplied by hours.
Worked example, watts to kWh
A 1,500 W space heater runs for 3 hours.
- Convert to kilowatts: 1,500 / 1,000 = 1.5 kW
- Multiply by the hours: 1.5 x 3 = 4.5 kWh
The heater draws at a rate of 1.5 kilowatts the whole time it is on. It accumulated 4.5 kilowatt-hours. Left running 3 hours a day for 30 days, the same heater accumulates 135 kWh.
Worked example, kWh to average kW
A bill says 900 kWh over a 30 day period. A 30 day period is 30 x 24 = 720 hours.
900 / 720 = 1.25 kW average
The building averaged 1.25 kilowatts across the whole month. Note the word average, because it is doing real work in that sentence. The month almost certainly did not run flat at 1.25 kW. It had a floor overnight and peaks during the day, and a monthly total cannot tell you where they fell. Only interval meter data can.
Common questions
What is the difference between kW and kWh?
kW measures power, the rate of draw at an instant, the way miles per hour measures speed. kWh measures energy, the accumulated amount, the way miles measures distance covered. A short, violent draw can be a large kW and a small kWh. A modest draw held all month can be a small kW and an enormous kWh. The full distinction, and why your bill charges them on separate lines by different logic, is in What is peak demand?.
How many watts are in a kWh?
This question has no answer as asked, and that is the point. Watts are a rate and kilowatt-hours are a quantity, so there is no fixed conversion between them without a duration. 1,000 watts held for one hour is 1 kWh. 100 watts held for ten hours is also 1 kWh.
How do I convert kWh to watts?
Divide the kilowatt-hours by the hours to get average kilowatts, then multiply by 1,000 for watts. 900 kWh over 720 hours is 1.25 kW, which is 1,250 W on average.
How many kWh does a 100 W bulb use?
100 W is 0.1 kW. Run for 5 hours it uses 0.5 kWh. Run for a 720 hour month it uses 72 kWh.
Is the kW on my bill the same as the average kW this calculator returns?
No, and confusing the two is expensive on a commercial bill. The kW line on a bill is usually peak demand: the single highest interval in the period, not the average across it. The average will always be lower, often several times lower.
Does the calculator convert MWh or Wh?
Not directly, but the steps are the same. 1 MWh is 1,000 kWh. 1 kWh is 1,000 Wh.
What this page does not do
It does not price anything. Converting units and pricing electricity are separate questions, and mixing them is how most calculators end up answering neither well. If you want the cost side, three other pages handle it properly: what a kilowatt-hour actually cost you last month, all in, is the one to start with.
