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Sources and Accuracy
Energy conversions use joule as the reference unit, including electrical, thermal, nutrition, and mechanical energy units.
Displayed results are rounded for readability. The calculator keeps enough precision for everyday use and switches to scientific notation for very large or very small values. Last reviewed: 2026-05-21.
About These Units
kilowatt-hour [kWh]
Definition
The kilowatt-hour is an energy unit equal to the energy used by one kilowatt of power for one hour.
History
Kilowatt-hours became common through electric utility metering and billing.
Current use
Kilowatt-hours are used for electricity bills, batteries, appliances, solar systems, and energy planning.
calorie [cal]
Definition
The calorie is an energy unit traditionally based on heating water by one degree Celsius.
History
Calories were used in heat measurement before joules became the SI standard.
Current use
Calories are used in nutrition, food labels, exercise estimates, and diet planning.