Watt-Hours Calculator — Energy & Electricity Cost
Find how much energy an appliance uses by entering its wattage and how long it runs. Get watt-hours (Wh) and kilowatt-hours (kWh), and optionally calculate the electricity cost from your tariff.
W
hours
$/kWh
Kilowatt-hours (kWh) used over the specified time
- 1
Energy in watt-hours
100 × 8 = 800Power (W) multiplied by time (h) gives watt-hours. - 2
Energy in kilowatt-hours
800 ÷ 1000 = 0.8000
How does this calculator work?
Watt-hours = Watts × Hours; divide by 1000 to get kWh. Enter wattage, hours of use, and your electricity tariff to instantly see energy consumed and estimated electricity cost. Works for any device: lights, appliances, EV chargers, solar panels.
Formula
How this is calculated
A watt-hour is the amount of energy consumed when a one-watt device runs for one hour. The formula is simply Energy = Power × Time: a 100 W bulb left on for 8 hours uses 800 Wh, or 0.8 kWh. Electricity bills are priced in kilowatt-hours, so dividing watt-hours by 1000 gives you the billing unit directly.
To estimate cost, multiply kWh by your electricity tariff (price per kWh). Tariffs vary widely by country, provider, and time-of-use — as of 2025 they range from roughly $0.08/kWh in parts of the US to $0.40/kWh in some European countries. The default here ($0.15/kWh) is a reasonable US average; edit it to match your bill.
The calculator assumes constant power draw over the full period. Real appliances cycle on and off (refrigerators, air conditioners), have standby modes, or vary load — so treat the result as an estimate. For intermittent use, model each appliance separately and sum the kWh.
Frequently asked questions
Watts measure power — the rate of energy flow at a given instant. Watt-hours measure energy — the total amount of power used over time. A 60 W bulb on for 10 hours consumes 600 Wh of energy.
Check the label on the appliance or its manual — it usually lists watts (W) or amps (A) and volts (V). If you see amps and volts, multiply them to get watts (W = A × V).
The average US household uses about 30 kWh per day (roughly 900 kWh/month). European homes tend to use less, around 10–15 kWh/day, due to smaller appliances and different climates.
Also known as
TG we-Calculate Editorial Team. (2026). Watt-Hours Calculator — Energy & Electricity Cost [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/watt-hours-calculator
TG we-Calculate Editorial Team. "Watt-Hours Calculator — Energy & Electricity Cost." TG we-Calculate. 2026. https://we-calculate.com/calculator/watt-hours-calculator.
TG we-Calculate Editorial Team, "Watt-Hours Calculator — Energy & Electricity Cost," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/watt-hours-calculator
@misc{wecalculate_watt_hours_calculator, title = {Watt-Hours Calculator — Energy & Electricity Cost}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/watt-hours-calculator}}, year = {2026}, note = {TG we-Calculate} }
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