What This Calculator Does
The Watts to kWh Calculator converts an appliance's power rating in watts (W) and the amount of time it runs in hours into the total energy it consumes, measured in kilowatt-hours (kWh). The kilowatt-hour is the standard unit shown on electricity bills worldwide, so this conversion lets you estimate exactly how much energy any device uses over a given period.
How to Use It
Enter the device's power draw in watts — usually printed on a label, nameplate, or in the manual. Then enter how many hours it runs. The calculator returns the energy used in kilowatt-hours, along with the equivalent value in watt-hours. To estimate cost, multiply the kWh result by your electricity rate (price per kWh).
The Formula Explained
The relationship is simple: $$\text{kWh} = \frac{\text{Power (W)} \times \text{Time (h)}}{1000}$$ Power in watts multiplied by time in hours gives energy in watt-hours. Because one kilowatt equals 1000 watts, dividing by 1000 converts watt-hours into kilowatt-hours. Energy is the product of how powerful a device is and how long it operates.
Worked Example
Suppose a 1500-watt space heater runs for 3 hours. $$\text{Energy} = \frac{1500 \times 3}{1000} = \frac{4500}{1000} = 4.5\ \text{kWh}$$ If electricity costs $0.15 per kWh, that session would cost about \(4.5 \times \$0.15 = \$0.68\).
FAQ
What is a kilowatt-hour? A kWh is the energy used by a 1000-watt device running for one hour. It is the unit utilities use for billing.
Do I need watts or kilowatts? Enter watts here. If you only know kilowatts, multiply by 1000 first (e.g. \(1.5\ \text{kW} = 1500\ \text{W}\)).
Can time be a fraction? Yes — enter decimal hours. For example, 30 minutes is 0.5 hours.
