What Is a kWh and How Is It Calculated?

What a kWh actually is

A kilowatt-hour is a unit of energy rather than power, and that is why many people confuse these two terms. Power is measured in watts or kilowatts, while energy is often measured in watt-hours or kilowatt-hours. A kilowatt-hour refers to one thousand watt-hours, and this unit equals one watt of power that is transferred within one hour.

Therefore, kilowatts represent the power in relation to the energy and time, while kilowatt-hours represent the amount of electricity that is consumed by an appliance when it works for an hour. To put it another way, kWh describes the magnitude of electricity consumption intensity, kW equals the amount of electricity consumed per hour, and this unit helps determine the amount of energy that was used in total.

The formula

Energy (kWh) = Power (kW) × Time (hours)

Or, if your appliance's wattage is listed in watts rather than kilowatts (which is more common), the formula looks like this:

kWh = (Watts × Hours) ÷ 1,000

Worked examples

Example 1 — A single appliance: A 1,500W space heater runs for 4 hours. kWh = (1,500 × 4) ÷ 1,000 = 6 kWh

Example 2 — A low-power device: A 60W fan runs for 10 hours. kWh = (60 × 10) ÷ 1,000 = 0.6 kWh

Example 3 — Working backwards from a bill: If your utility charges you for 30 kWh used in a day by a 1,250W appliance, you can find the hours it ran: Hours = (30 × 1,000) ÷ 1,250 = 24 hours

Example 4 — A power station: A 1,000Wh power station is the same as 1 kWh of stored energy. If it powers a 100W laptop, it could theoretically run it for around 10 hours (1,000Wh ÷ 100W), before accounting for efficiency losses.

Why kWh is the unit your electricity bill uses

Unlike a standard electricity meter, a utility company does not charge you for the power you are currently using measured in Watts, but for the amount of power (in kWh) you have used during a billing period. Your meter is simply a cumulative measure of your electricity consumption, and your bill is calculated by multiplying that number by a coefficient (your electricity rate) that depends on your location and electricity provider.

That’s why your overnight 10 W modem-router may cost as much as a brief 1000 W hair-dryer usage.

kWh vs Wh — what's the difference?

Frequently asked questions

What does 1 kWh actually mean?

1 kW hour means 1000 Watt energy was transferred during 1 hour. It can also mean 100 Watt during 10 hours or 2000 Watt during 0,5 hours. Any amount of Watts multiplied by hours gives kW hour.

How do I calculate kWh from watts?

Take the appliance's wattage and multiply it by the number of hours it runs, then divide by 1,000. For instance, your 1,500W heater running for 4 hours would equal 1,500 x 4 / 1,000 = 6 kWh.

How much does 1 kWh cost?

It depends on your local electricity rate. This may vary depending on your country, state, and electricity provider. Your electricity bill or your provider's website will state how much you are being charged for each kilowatt-hour (kWh) of electricity, typically in cents or your local currency per kWh.

Is a power station's Wh rating the same as kWh?

Yes, only the scale is different. The 'Wh' and 'kWh' stand for watt-hours and kilowatt-hours, respectively, with the latter being larger than the former by 1,000 times. This means that a 1,000Wh power station is equal to 1 kWh.

How many kWh does a house use per day?

It depends on your household, how cold or hot it is where you are and what appliance you have. But generally households use about 20-30 kWh per day. The best way to tell how much electricity you use is to look at the bill you get every month.