Watt to kWh Calculator

How to use the watt to kwh calculator

Enter a device’s power in watts and the number of hours it runs, and you get the energy it uses in kilowatt-hours. This is the single most useful energy conversion there is, because every electricity-cost figure starts here — you turn watts and time into kilowatt-hours first, then put a price on the kWh. Power is the rate you’re drawing electricity; a kilowatt-hour is the accumulated total once that rate has run for a while.

The relationship is direct: energy is power multiplied by time. A 1,000 W device running for one hour uses 1 kWh; run the same device for five hours and it uses 5 kWh. Watts tell you how hard electricity is flowing right now, and kilowatt-hours tell you how much has flowed in total. Stretch the time and the energy climbs in step; the watts never change, only the hours do.

This is the forward, everyday direction — power and time in, energy out — which is what you almost always want. It’s the opposite of the kWh-to-Watts tool, which works backward from a known energy total over a known span to recover the average power behind it. Use this one when you know what a device draws and how long it runs; use that one when you have a meter reading and want the steady load that produced it.

It’s the building block behind every cost calculation, so reach for it whenever you want to size up an appliance, a habit, or a whole circuit. A space heater you leave on, a server humming all day, an old fridge — read the watts off the label, estimate the hours, and you have the kilowatt-hours. From there the energy is comparable across devices no matter how their wattages differ, which is what makes the kWh the honest unit for stacking one thing against another.

To turn that energy into money, multiply the kilowatt-hours by your electricity rate — there’s no rate field here because this tool is a pure units conversion, not a bill. The Electricity Cost Calculator does the multiplication for you and applies your rate to the kWh, which is the natural next step once you know the energy.

The formula

Energy is power multiplied by time. Watts are divided by 1,000 to land in kilowatts before multiplying by the hours:

kWh = (watts ÷ 1000) × hours

Worked example with the defaults — 1,000 W run for 5 hours: 1,000 ÷ 1000 × 5 = 5 kWh. The 1,000-watt device draws one kilowatt, and one kilowatt sustained for five hours is five kilowatt-hours.

A couple more to anchor it: 1,500 W for 24 hours is 36 kWh, and a 60 W bulb for 10 hours is 0.6 kWh. It is the single most useful energy conversion — every electricity-cost figure starts by turning watts and time into kilowatt-hours, and only then multiplying the kWh by a rate to reach dollars.

Frequently asked questions