Device Details
Energy Usage
Estimated Cost
Formula: kWh = (Watts × Hours) ÷ 1000. Cost = kWh × rate ($/kWh).
How to Use This kWh Calculator
Enter the device power in watts or kilowatts, then add the number of hours the device runs each day and the number of days it runs each month. The calculator converts those values into daily, monthly, and yearly energy usage in kilowatt-hours.
You can also enter your electricity rate in dollars per kWh to estimate operating cost. This makes it useful for comparing appliances, checking the impact of longer run times, and estimating how much a heater, air conditioner, computer, or lighting circuit adds to your electric bill.
What kWh Means
A kilowatt-hour (kWh) is a measure of energy use over time. It is different from kilowatts (kW), which describe power at a moment in time. For example, a 1 kW appliance running for 1 hour uses 1 kWh of electricity.
Utility bills are typically based on total kWh consumed during the billing period, which is why converting watts and run time into kWh is useful when estimating appliance energy usage and monthly electricity cost.
What Affects Electricity Usage
Electricity consumption depends on both device power and how long the device runs. Higher wattage appliances use more electricity per hour, while longer run times increase total monthly and yearly energy consumption.
Real-world usage can also vary based on cycling behavior, thermostat settings, efficiency, ambient temperature, and how heavily a device is loaded. Refrigerators, air conditioners, dehumidifiers, pumps, and heaters often do not run at full power every minute of the day.
Common kWh Calculator Uses
This calculator is commonly used to estimate electricity usage for space heaters, refrigerators, window AC units, computers, gaming PCs, TVs, pool pumps, electric water heaters, EV charging, and household lighting. It is also useful when comparing the energy cost of running two different appliances.
For related planning, you can also check our electricity cost calculator, wire size calculator, and voltage drop calculator.
Frequently Asked Questions
To calculate kWh, multiply watts by hours used and divide by 1000. For example, a 1000W device used for 3 hours consumes 3 kWh.
kW measures power, while kWh measures energy used over time. A device rated at 1 kW uses 1 kWh of electricity when it runs for one hour.
A 1500W heater uses 1.5 kWh per hour. If it runs for 8 hours in one day, it uses 12 kWh.
A modern refrigerator often uses roughly 30 to 60 kWh per month, depending on size, efficiency, temperature settings, and how often the compressor runs.
Multiply your energy use in kWh by your electricity rate in dollars per kWh. For example, 100 kWh at $0.16 per kWh costs about $16.
A 100W bulb uses 0.1 kWh for every hour it runs. If used for 5 hours per day, it consumes 0.5 kWh per day.