Give power and energy different jobs
The EIA explains the distinction between power and accumulated energy. A watt is a unit of power; a kilowatt is 1,000 watts. A kilowatt-hour is the energy associated with one kilowatt maintained for one hour.
That is why an appliance label and an electricity bill usually show different units. The appliance’s watt figure describes an input rate or rating. The bill’s kWh quantity describes energy over a period. Neither number tells you cost until the relevant tariff and operating assumptions are attached.
Work through one conversion
Imagine an appliance draws a constant 650 W for two hours. First, 650 ÷ 1,000 = 0.65 kW. Then 0.65 × 2 = 1.3 kWh. At an illustrative $0.18/kWh, the cost is 1.3 × $0.18 = $0.234, or about 23 cents.
Do not divide by 1,000 a second time when the figure is already in kilowatts. Also, “kW per hour” is not the unit needed for this cost calculation. The result is kilowatt-hours because power is multiplied by elapsed hours.
See why a larger wattage is not always a larger bill
A constant 100 W appliance used for ten hours consumes 1 kWh. A constant 1,000 W appliance used for one hour also consumes 1 kWh. At the same tariff, each costs $0.18 in this hypothetical comparison.
This does not make the appliances interchangeable; they may do different jobs. It shows why comparing watt labels without operating time can mislead. For an appliance that cycles or varies output, use measured energy or a suitable average draw rather than assuming the rated power persists throughout.
Keep minutes, days and money consistent
Convert minutes by dividing by 60. Fifteen minutes is 0.25 hours, so a constant 800 W draw for that period uses 0.2 kWh. At $0.18/kWh, it costs $0.036. Repeating the session on 30 days costs $1.08 when rounded at the end.
Label every line of a calculation with its units and period. If a tariff is listed in cents, convert it to dollars before entering a dollars-per-kWh field: 18 cents is $0.18. The running cost calculator follows this sequence, but you still supply the schedule and a suitable power input. Correct units make assumptions visible; they do not turn a hypothetical input into a measurement.
Choose your next step
Continue with the question that matches your next decision:
Sources & further reading
Numerical examples are illustrative unless explicitly described as measured. This guide does not claim hands-on product testing. Read the methodology and editorial disclosure.