How to use this calculator
Use the appliance’s average power draw while operating. Enter how many hours it runs each day, the number of days, and the per-kWh rate on your electricity bill. An energy meter can provide a better average for cycling equipment.
The formula
A worked example
A 100 W device used 8 hours a day for 30 days uses 24 kWh. At $0.15 per kWh, it costs $3.60.
Assumptions & limitations
Assumes a constant entered average draw and flat rate. Excludes fixed charges, tiered pricing, time-of-use changes, demand charges, and taxes. Rated maximum power may overstate typical use.
Common questions
Can I use the number on the power adapter?
It may be a maximum rating, not actual consumption. Use a measured average when possible.
Does this include my whole bill?
No. It estimates the variable energy cost of the entered load only.
Supporting reference
The method above states this calculator’s assumptions. This reference provides related definitions and technical context.
U.S. Energy Information Administration: measuring electricity ↗Formula and worked example checked against automated test cases. About our methodology.