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Kilojoules, kilocalories, kilowatt-hours and megajoules.
Choose a conversion below. Every tool includes an instant result, an example and a short explanation.
Energy measures the capacity transferred or used in a process. The joule is its SI unit. Food labels often use kilocalories, while electricity bills use kilowatt-hours and engineering reports may use megajoules. These are units of the same quantity, so a unit change lets you compare figures without changing what happened physically.
This category uses 1 kilocalorie = 4,184 joules, the thermochemical convention common for food energy. Other historical calorie definitions differ slightly, so read the source if metrology-level precision matters. A kilowatt-hour is energy accumulated when one kilowatt of power continues for one hour; it is not a rate or a power rating by itself.
A watt is one joule per second, so a kilowatt used continuously for one hour represents 3.6 million joules, or one kilowatt-hour. Energy is an accumulated quantity; the same total can come from a low power over a long time or a high power over a short time.
Nutrition labels often use “Calorie” with a capital C to mean one kilocalorie, or 1,000 small calories. Check the label and the selected unit before comparing food energy with joules. This category distinguishes the units; it cannot guess whether an unlabeled “calorie” was used in the nutritional or thermochemical sense.