Watts vs Watt-Hours (W vs Wh): Power and Energy Explained
Watts and watt-hoursW, Wh and kWh
Watts (W) measure power, how fast electricity is used at a moment. Watt-hours (Wh) measure energy, power used over time; 1,000 Wh is a kilowatt-hour (kWh).
- Height: power, in watts (W), how fast energy flows right now
- Area: energy, in watt-hours (Wh), power × time
At a glance
- Watt (W)
- Power at a moment
- Watt-hour (Wh)
- One watt used for one hour
- Kilowatt-hour (kWh)
- 1,000 Wh, the unit on your electric bill
- Example
- A 40 W bulb on for 5 hours uses 200 Wh, or 0.2 kWh
- Average US home
- About 899 kWh a month (2022)
The EIA’s explainer puts it in one line: watts measure power at a specific moment, and watt-hours measure how much electricity is used over a period of time. One watt-hour is the energy of one watt used for one hour. Its example: a 40 W light bulb on for five hours uses 200 Wh, or 0.2 kWh.
Which number matters for plug-in solar?
Both, for different questions. The watts on a kit, and the 1,200 W cap in laws like California’s, are the most it can deliver at once, in full sun. What it saves depends on watt-hours: how much it makes over a day and a year, which depends on your sun, direction and shade. For scale, the average US home used about 899 kWh a month in 2022, according to the EIA. Our plug-in solar calculator turns watts into kilowatt-hours for your city.
And for a power station?
The same split. Its capacity in Wh says how long it can run things; its output in W says how much it can run at once. Our power station sizer works out both from the appliances you pick.
Published by the Plugged Sun editorial team
Related terms
Sources
- Measuring electricity (Official document, US Energy Information Administration, 2026)
- How much electricity does an American home use? (Official document, US Energy Information Administration, 2024)