What Is a Kilowatt Hour?

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A kilowatt-hour (kWh) is a unit of energy. The U.S. Energy Information Administration defines it as “a unit of work or energy,” measured as “1 kilowatt (1,000 watts) of power expended for 1 hour.” Electric bills use kWh because the utility charges for the total energy used over time, not for the instantaneous power. The short answer is that a kWh is what your meter adds up on each bill.

Quick answer

• One kWh is 1,000 watts used for one hour.
• A watt measures power, the rate of energy use. A kWh measures energy, the total used over time.
• To estimate kWh for a device, multiply its power in kilowatts by its hours of use.
• Electrical work on mains circuits can kill. Use a meter whose CAT rating suits the circuit, and leave panel work to a licensed electrician.

Power and energy are different

Power is how fast energy is used. Energy is the total amount used. Fluke’s glossary defines kilowatt-hour as “the use of one thousand watts for one hour.” The word “hour” is the key: the unit tracks time as well as power.

A 100 W bulb running for 10 hours uses 1,000 watt-hours, which is 1 kWh. A 1,000 W heater running for 1 hour also uses 1 kWh. The two appliances draw power at different rates, but they use the same energy.

The kilo prefix

The “kilo” in kilowatt-hour is a metric prefix. NIST’s list of SI prefixes gives the prefixes deka, hecto and kilo as “meaning, respectively, 10, 100, and 1000.” So one kilowatt is 1,000 watts, and one kilowatt-hour is 1,000 watts held for one hour. Watt-hours are the same idea without the prefix: 1,000 Wh equals 1 kWh.

How to estimate kWh for a device

Use this method:

1. Find the power rating of the device in watts, on its label or in its manual.
2. Divide by 1,000 to get kilowatts.
3. Multiply by the number of hours it runs.

Example: a 500 W space heater running for 4 hours uses 0.5 kW x 4 h = 2 kWh. The result is an estimate. Real devices vary in how long they draw their rated power, and some draw less than their label value.

Where a multimeter fits

A basic multimeter measures volts, amps and resistance. It does not read kWh on its own. You can use volts and amps readings to estimate watts for a resistive load, then apply the time to get energy. A utility meter or a dedicated energy monitor is the tool for an actual kWh total. Check the listing of any meter before you assume it reads energy.

How we chose the sources

We opened three sources on 2026-10-27: the EIA Energy Glossary entry for kilowatthour, the Fluke electrical glossary, and the NIST page on metric (SI) prefixes. We quote the definitions directly. We did not use retail pages or product listings to define the unit.

What we could not verify

The sources we opened do not give typical kWh figures for any appliance, so this article gives none. They also do not say how a particular utility calculates its charges. Your bill and your utility’s tariff set the actual cost.

Frequently asked questions

Is a kWh the same as a kW?

No. A kilowatt is a unit of power. A kilowatt-hour is a unit of energy, equal to one kilowatt used for one hour.

How many watt-hours are in a kilowatt-hour?

There are 1,000 watt-hours in one kilowatt-hour, because kilo means 1,000.

Does a higher wattage always mean higher kWh?

Not on its own. Energy depends on both the power and the time it runs.

Can I measure kWh with a multimeter?

Not directly. A multimeter reads volts, amps and resistance. A utility meter or energy monitor is designed to total energy over time.

Is kWh the unit I pay for?

Electric bills usually charge by kWh. Check your own bill and tariff for the rate and any fixed charges.

Bottom line

A kilowatt-hour is the energy used by 1,000 watts over one hour. Multiply a device’s kilowatts by its hours to estimate its kWh.

Related guides

• Best multimeters for home use, for basic meters and their safety ratings.
• Best true RMS multimeters, for meters that read non-sinusoidal AC more reliably.

Sources

• U.S. Energy Information Administration, “Glossary: kilowatthour,” https://www.eia.gov/tools/glossary/index.php?id=kilowatthour (opened 2026-10-27)
• Fluke, “Electrical Glossary,” https://www.fluke.com/en-us/learn/blog/electrical/electrical-glossary (opened 2026-10-27)
• NIST, “Metric (SI) Prefixes,” https://www.nist.gov/pml/owm/metric-si-prefixes (opened 2026-10-27)