How to convert watts to kWh

How to convert electric power in watts (W) to energy in kilowatt-hour (kWh).

You can calculate kilowatt-hour from watts and hours. You can't convert watt to kilowatt-hour unit since watt and kilowatt-hour unit represent different quantities.

Watts to kilowatt-hour calculation formula

The energy E in kilowatt-hour (kWh) is equal to the power P in watts (W), times the time period t in hours (hr) divided by 1000:

E_(kWh) = P_(W) × t_(hr) / 1000

So

kilowatt-hour = watt × hour / 1000

or

kWh = W × hr / 1000

Example 1

What is the energy consumption in watt-hour when the power consumption is 5000 watts for time duration of 3 hours?

E = 5000W × 3h / 1000 = 15 kWh

How to convert kWh to watts »

Example 2

Let’s find the kWh of 1,500 watts for 2.5 hours.

kWh = (1,500 × 2.5) ÷ 1,000
kWh = 3,750 ÷ 1,000
kWh = 3.75

Example 3

Let’s predict how much it costs to power a light bulb every hour. A 100 watt light bulb uses 100 watts of power. To convert the power in watts to kilowatt-hours, multiply 100 watts by 1 hour, then divide by 1,000 to find the energy usage in kWh.

Energy = (100 × 1) ÷ 1,000
Energy = 100 ÷ 1,000
Energy = 0.1 kWh

If electricity costs $0.12 per kWh, then a 100 watt light bulb will cost 1.2 cents per hour that it’s on.