Published October 23, 2026 · By RegionalRates
kW measures power. kWh measures energy. Power tells you how fast a device is using electricity at a moment. Energy tells you how much it used over time. You need both power and operating time to estimate a cost.
The units on your equipment and bill
| Unit | Meaning | Example |
|---|---|---|
| W: watt | A unit of power | A device drawing 100 W |
| kW: kilowatt | 1,000 watts of power | 1,500 W = 1.5 kW |
| kWh: kilowatt-hour | Energy used over time | 1.5 kW for 2 hours = 3 kWh |
The U.S. Energy Information Administration explains electricity consumption in kilowatt-hours. The letters matter: 1.5 kW is a power level, while 1.5 kWh is an amount of energy. A device does not have to run for exactly one hour to use a kilowatt-hour.
Convert watts and hours into kWh
For a device using a constant 100 watts for five hours, divide 100 by 1,000 to get 0.1 kW, then multiply by five. The result is 0.5 kWh. At an illustrative $0.16 per kWh, that energy costs $0.08.
A 1,500-watt device running at full power for 20 minutes uses the same 0.5 kWh: 1.5 kW × one-third of an hour. A higher power draw does not automatically mean higher total consumption if the operating time is shorter.
How the rate turns energy into dollars
Or: kWh × price in cents per kWh ÷ 100
At an illustrative 16 cents per kWh, 300 kWh costs $48 in energy charges. It does not cost $4,800: the cents-to-dollars conversion is necessary. In RegionalRates calculators, enter 16 for a price of $0.16/kWh.
A full bill may also contain fixed charges, taxes, and other price components. Those do not disappear when you calculate kWh. Use the electricity bill calculator to include a separate fixed charge, and follow our bill-reading guide to avoid double-counting.
Why nameplate watts can overstate a monthly estimate
An appliance's listed power is not necessarily its average draw across every hour it is connected. A refrigerator cycles, a heater's thermostat switches its element, and equipment with variable speeds can operate at different power levels. Read the equipment documentation rather than assuming the largest printed number applies continuously.
If a monitor records 12 kWh over five representative days, the measured daily average is 2.4 kWh. Projecting that pattern across 30 days gives 72 kWh and $11.52 at 16 cents. This remains a projection: a different season or schedule could change it.
Does 1 kWh tell me how long an appliance ran?
Only if you know its average power during that time. At a constant 1 kW, 1 kWh corresponds to one hour. At 0.25 kW, it corresponds to four hours. At 2 kW, it corresponds to half an hour. With changing loads, use the monitor's cumulative energy reading instead of a single instant of power.
What if my bill includes a kW demand charge?
Some tariffs charge separately for demand. That charge is based on a defined power measurement, not simply your total monthly kWh. Read the tariff's measurement interval, rate, and conditions. Our flat-rate bill calculator does not model demand charges or time-of-use schedules.
Put the units to work
- Use the appliance calculator when you have a suitable power estimate and operating schedule.
- See a complete space-heater running-cost example.
- Learn when a plug-in or panel monitor is more useful than estimating watts.
Source and assumptions
Unit definitions: U.S. EIA: Measuring electricity. All device powers, rates, and schedules on this page are illustrative RegionalRates calculations. They are not equipment specifications or live electricity prices.