What This Calculator Does
This tool converts an appliance's power rating in watts (W) and the number of hours it runs into the energy it consumes in kilowatt-hours (kWh). kWh is the unit your electricity provider uses for billing, so knowing it lets you estimate the running cost of any device.
How to Use It
Enter the device's power draw in watts (check the label or spec sheet) and how many hours it operates. The calculator instantly returns the energy used in kWh and watt-hours. To find the cost, multiply the kWh result by your electricity rate (price per kWh).
The Formula Explained
Energy equals power times time. Power is measured in watts and time in hours, giving watt-hours. Dividing by 1000 converts watt-hours to kilowatt-hours:
$$\text{kWh} = \frac{\text{Watts} \times \text{hours}}{1000}$$
One kilowatt equals 1000 watts, which is why the division by 1000 is needed.
Worked Example
Suppose a 1500 W space heater runs for 4 hours. The energy used is $$(1500 \times 4) \div 1000 = 6000 \div 1000 = 6 \text{ kWh}.$$ If electricity costs $0.15 per kWh, that session costs \(6 \times \$0.15 = \$0.90\).
FAQ
What is a kilowatt-hour? A kWh is the amount of energy used by a 1000-watt device running for one hour. It is the standard unit on electricity bills.
Where do I find a device's wattage? Look at the rating label, power supply, or manual. If only volts and amps are listed, multiply them (\(\text{W} = \text{V} \times \text{A}\)).
How do I get the cost? Multiply the kWh result by your utility's price per kWh.
