The core formula
Divide watts by 1,000 to get kilowatts. Multiply by operating hours to get kWh, then multiply by your all-in variable electricity price.
Use realistic runtime
A refrigerator, air conditioner or sump pump cycles. The label wattage multiplied by 24 hours usually overstates consumption. A plug-in meter or smart-device history can provide average draw.
Separate fixed charges
A fixed monthly customer charge does not increase when one appliance runs longer. Leave it out of marginal appliance decisions, but include it when estimating the entire bill.
Worked example: watts to monthly dollars
A 600-watt device used for three hours per day consumes 0.6 kW × 3 hours × 30 days = 54 kWh per month. At an entered variable price of $0.16 per kWh, the usage portion is $8.64.
That result is a scenario, not a promise. A cycling appliance may draw less than its label rating for part of the hour, while standby power or a second operating mode may add consumption.
Use measured average power and runtime when the purchase or repair decision is material; use label wattage only as a clearly identified planning bound.
Primary sources and scope
These links support the units or diagnostic method used above. They do not replace your provider’s current tariff, bill or safety instructions.
- EIA — Measuring electricity ↗ — Defines one kWh as one kilowatt used for one hour.
- EIA — Electricity prices and locality ↗ — Explains why electricity prices vary by locality and customer context.
This guide explains general billing math. Utility tariffs and local rules control your actual charges. Sources and update practices are documented in our methodology.
Read the methodology →