What Is a Watt-hour Calculator?
A watt-hour (Wh) is a unit of energy equal to one watt of power sustained for one hour. This calculator turns a device's power draw and how long it runs into the total energy it consumes, expressed in both watt-hours and kilowatt-hours (kWh). Because electricity bills are charged in kWh, knowing the watt-hours of an appliance helps you estimate running costs and compare devices.
How to Use It
Enter the device's power rating in watts (found on its label or spec sheet) and the number of hours it runs. The calculator multiplies the two to give energy in watt-hours, then divides by 1000 to show kilowatt-hours. For minutes, convert to hours first (e.g. 30 minutes = 0.5 h).
The Formula Explained
The core relationship is $$\text{Wh} = \text{P (W)} \times \text{t (h)}$$ Power measures the rate of energy use in watts; multiplying by the time in hours gives total energy. To get kilowatt-hours, divide by 1000: $$\text{kWh} = \text{Wh} \div 1000$$
Worked Example
A 60 W light bulb left on for 5 hours uses $$60 \times 5 = 300 \text{ Wh}$$ which is $$300 \div 1000 = 0.3 \text{ kWh}$$ If your electricity costs $0.15 per kWh, that's about 4.5 cents of energy.
FAQ
What's the difference between watts and watt-hours? A watt is power (rate); a watt-hour is energy (amount used over time).
How do I convert Wh to kWh? Divide watt-hours by 1000.
Can I use minutes instead of hours? Convert minutes to hours by dividing by 60, then enter that value.
