SuperCalX

kW vs kWh: What Is the Difference?

By Dr. Ahmed Mortuza Saleque · Updated · How we check our content

The short answer

A kilowatt (kW) measures power: how fast electricity is being used at one moment. A kilowatt-hour (kWh) measures energy: how much was used over time. Energy = power × time, so a 2 kW heater running for 3 hours uses 6 kWh. Your electricity bill charges for kWh, not kW.

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Diagram comparing kilowatts as a rate of flow with kilowatt-hours as the amount collected, with a 2 kW heater running 3 hours using 6 kWh
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A simple way to picture it

Think of filling a bath. The tap's flow rate is like kilowatts: how fast water arrives. The water in the bath is like kilowatt-hours: how much has arrived. A powerful tap fills the bath quickly; a weak one takes longer to deliver the same amount.

A car works the same way: speed is like kW and distance travelled is like kWh. Driving 60 mph for 2 hours covers 120 miles; running 2 kW for 3 hours uses 6 kWh.

The formula

You wantFormulaExample
Energy (kWh)power (kW) × time (h)2 kW × 3 h = 6 kWh
Power (kW)energy (kWh) ÷ time (h)6 kWh ÷ 3 h = 2 kW
Time (h)energy (kWh) ÷ power (kW)6 kWh ÷ 2 kW = 3 h
Watts to kilowattswatts ÷ 1,0001,500 W = 1.5 kW

The power calculator handles these conversions, and the energy converter turns kWh into joules, BTU or calories. One kWh is 3.6 million joules.

What 1 kWh looks like

  • A 1,000 W microwave running for 1 hour.
  • A 100 W television running for 10 hours.
  • A 10 W LED bulb running for 100 hours.
  • A 2 kW kettle running for 30 minutes.

At $0.16 per kWh, each of those costs 16 cents. See how to calculate electricity cost for a table of common appliances.

On your electricity bill

Homes are billed for energy in kWh. A bill showing 900 kWh at $0.16 is $144 before fixed charges. Some business tariffs add a demand charge based on the highest kW drawn in the month, because the grid has to be built for that peak.

Solar panels, batteries and electric cars

A solar system's size is given in kW: the most it can produce at once. Its output over a day is in kWh. An 8 kW system with 5 peak sun hours produces about 32 kWh a day after typical losses; the solar panel guide explains the sizing.

Batteries are the reverse: capacity is in kWh and the charger's speed is in kW. A 60 kWh car battery on a 7 kW home charger takes about 60 ÷ 7 = 8.6 hours to fill from empty, and costs about $9.60 at $0.16 per kWh.

Common questions

Is kWh the same as kW per hour?

No. A kilowatt-hour is kilowatts multiplied by hours, not divided. "kW per hour" would describe how quickly power is changing, which is rarely what people mean.

How many kWh does a 1 kW appliance use?

1 kWh for every hour it runs at full power. Run it for 4 hours and it uses 4 kWh.

How do I convert kWh to kW?

Divide by the hours. 12 kWh used over 4 hours is an average of 3 kW.

How many kWh does a house use per day?

A home using 900 kWh a month averages 30 kWh a day, which is a steady 1.25 kW around the clock.

Calculators for this article

Sources

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