Start with energy, not power
A kilowatt-hour measures energy. Annual kWh therefore describes an amount of electricity over a year. It is different from watts, which describe power at a moment.
To estimate annual appliance energy cost, multiply annual kWh by cents per kWh and divide by 100. For example, 700 kWh/year × 16.5¢/kWh ÷ 100 = $115.50/year.
Convert the annual estimate
LabelWatts uses two simple average-period conversions:
- Monthly average = annual estimate divided by 12.
- Weekly average = annual estimate divided by 52.
These are comparison conveniences. Calendar months vary in length, a year is not exactly 52 weeks, and many appliances have seasonal usage. The conversions do not predict a particular billing period.
Keep the unit beside the number
Write kWh/year, ¢/kWh, and $ per year beside inputs and results. A number without its unit is easy to misread. The substituted formula in the calculator keeps each unit visible so you can check the path from input to estimate.