Watts to kWh Calculator

A device's power rating in watts tells you how fast it uses electricity — but multiply that by time, and you get energy consumption in kilowatt-hours (kWh), the unit your electricity bill is based on. Enter your device's power and time (in milliwatts, watts, or kilowatts; seconds, minutes, or hours) into the Watts to kWh Calculator to see your energy consumption in kWh and Wh, plus projected daily and monthly energy use. Also try the kWh to Watts Calculator.

W

Power rating of the appliance or device

hours

Duration the device is used

Results

Energy Consumption

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Energy in Watt-hours

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Daily Energy (24 hours)

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Monthly Energy (30 days)

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Results Table

Frequently Asked Questions

How do you convert watts to kilowatt-hours (kWh)?

To convert watts to kWh, multiply the power in watts by the time in hours, then divide by 1,000. The formula is: Energy (kWh) = Power (W) × Time (hours) ÷ 1,000.

What's the difference between watts and kilowatt-hours?

Watts (W) measure power - the rate of energy consumption at any moment. Kilowatt-hours (kWh) measure energy - the total amount of power used over time. Think of watts as speed and kWh as distance traveled.

How much does it cost to run a 1500W appliance for 8 hours?

A 1500W appliance running for 8 hours consumes 12 kWh (1500 × 8 ÷ 1000). At an average electricity rate of $0.12 per kWh, this would cost approximately $1.44.

Why is kWh important for electricity bills?

Electric utility companies charge customers based on kilowatt-hours consumed, not watts. Your monthly bill shows total kWh usage multiplied by your rate per kWh, making this conversion essential for estimating costs.

Can I convert other power units to kWh?

Yes, you can convert kilowatts (kW) to kWh by multiplying by time in hours. For milliwatts, first convert to watts by dividing by 1,000, then use the standard formula.

How do I calculate annual energy consumption?

Calculate daily kWh consumption first, then multiply by 365 days. For seasonal appliances, multiply daily usage by the number of days used per year instead of 365.