Electrical calculator

Energy Use Calculator

Estimate daily, monthly, and annual appliance electricity use in watt-hours and kilowatt-hours.

Estimate appliance electricity use

Multiply a device’s input power by its operating time to estimate energy. Dividing watt-hours by 1,000 converts the result to kilowatt-hours, the unit commonly shown on an electric bill.

Worked example

One 1,500 W device used for two hours per day consumes 3,000 Wh, or 3 kWh, per day. At 30 days per month, that is 90 kWh. The annualized daily pattern equals 1,095 kWh.

Improve the estimate

• Use measured average watts for devices that cycle or change modes; a plug-in meter may be more accurate than maximum nameplate power.
• Count standby consumption if the device remains energized outside its active hours.
• For several identical devices, multiply by quantity. For different devices, calculate each separately and add the kWh.
• To estimate cost, multiply kWh by the full applicable electricity rate or use the linked Electricity Cost Calculator.

Frequently asked questions

What is a kilowatt-hour?

A kilowatt-hour is 1,000 watt-hours of energy. One kilowatt used for one hour, or 100 watts used for ten hours, each equals 1 kWh in the ideal calculation.

Should I use input or output watts?

For electricity consumption, use electrical input power. Output ratings may omit losses and can substantially understate energy drawn from the outlet.

Why does my bill differ?

Bills include all loads plus possible fixed charges, taxes, time-based rates, and utility adjustments. Equipment also cycles and rarely operates exactly at its labeled maximum for a fixed daily duration.

How to get a dependable result

• Use nameplate ratings or manufacturer specifications when they are available.
• Keep every input in the unit shown beside its field.
• Treat calculated values as planning estimates; real equipment, batteries, and conductors have losses, tolerances, and operating limits.

Related calculators

Sources and review notes

The U.S. Department of Energy explains estimating appliance energy use and converting watt-hours to kilowatt-hours.

Last reviewed September 2026. Results are educational estimates and do not replace product instructions, electrical codes, engineering review, or professional advice.