kWh Calculator โ Energy & Cost
Calculate kilowatt-hours from watts and time, estimate cost, and convert kWh to Wh, MJ, BTU, kcal and therms.
๐ Runs entirely in your browser โ nothing is uploadedWhat a kilowatt-hour is
A kilowatt-hour (kWh) is the unit your electricity bill uses. It is the energy consumed by a 1,000-watt appliance running for one hour. Because power (kW) and energy (kWh) are easy to confuse, remember the difference: power is how fast energy is used, energy is the total used over time. A 2 kW heater has the same power whether it runs for a minute or a day, but it consumes 2 kWh in one hour and 48 kWh in a day.
Calculating energy use
The formula is simple: kWh = kW ร hours, or watts รท 1,000 ร hours. This calculator accepts power in watts, kilowatts or horsepower, and time in minutes, hours or days, so you can enter a microwave rated 900 W for 20 minutes or a pump rated 2 hp for a whole day. Multiply by the number of identical devices and, if you add your price per kWh, you get the cost directly. For realistic estimates remember that many appliances, such as refrigerators and heaters, cycle on and off, so their average power is lower than the label rating.
Converting between energy units
Switch to converter mode to translate an energy figure into every other common unit: watt-hours, megawatt-hours, joules, kilojoules, megajoules, BTU, kilocalories and therms. Useful equivalents are 1 kWh = 3.6 MJ = 3,412 BTU = 860 kcal. Gas bills often use therms or cubic metres, heating equipment is rated in BTU per hour, and food energy is given in kilocalories, so a converter makes it easy to compare fuels on a like-for-like basis.
To go further, use the electricity cost calculator for daily, monthly and yearly running costs, or the watts, amps and volts calculator to find a device's power from its current and voltage. All figures are computed in your browser.
How to use
- Choose a modeUse โEnergy usedโ to turn power and time into kWh, or โConvert energy unitsโ to switch between kWh, MJ, BTU and others.
- Enter power and timeType the device power in watts, kilowatts or horsepower and how long it runs. Add the number of devices and an optional price per kWh.
- Read the energy and costSee kilowatt-hours, watt-hours, megajoules, BTU and the cost.