Energy Unit Converter

Convert between joules, calories, kilocalories, BTU, kWh, and electron volts.

Tested tool guide Tested browser tools Checked August 16, 2026

What Energy Unit Converter does, with a checked example

Energy Unit Converter expresses one amount of energy in another supported unit: joules, calories, kilocalories, British thermal units, kilowatt-hours, or electron volts. Enter a numeric amount, identify its current unit, and choose the unit needed for the result. The physical quantity remains energy; only its numerical scale and unit change. A frequent mistake is treating calories and kilocalories as interchangeable. One kilocalorie equals 1,000 calories, and the capitalized Calorie commonly used for food energy refers to a kilocalorie.

Worked example

A concrete input and expected output from the current implementation.

Input

1 kWh to joules

Expected output

3,600,000 J

One kilowatt is 1,000 joules per second, and one hour is 3,600 seconds. Multiplying 1,000 by 3,600 gives exactly 3,600,000 joules.

How the result is produced

Unit-to-unit conversion

The source selection tells the converter how to interpret the entered number, while the target selection determines the result's unit. It rescales the same energy quantity through the relationship between the two units. For example, converting kWh to joules changes neither the underlying energy nor its physical meaning. It only replaces the value and unit with an equivalent representation.

Scale and symbol handling

Unit names and prefixes are significant. A kilocalorie is 1,000 calories, while a kilowatt-hour is an energy unit formed from power multiplied by time. The symbol eV denotes electron volts, which are useful for atomic-scale energies despite producing very small joule values. Scientific notation may therefore be more readable when converting between electron volts and macroscopic units such as kWh.

Good uses

Convert an appliance or battery energy figure from kWh to joules for use in an SI-based calculation.
Translate a heat quantity reported in calories, kilocalories, or BTU into the unit used by another specification.
Express an atomic or particle energy stated in electron volts as joules, or convert a joule value back to eV.

Limits and checks

Do not enter a nutrition-label Calorie as a small calorie. Use kilocalories when the stated Calories represent food energy.
Calorie and BTU definitions have recognized variants. For contractual, laboratory, or high-precision work, confirm that the converter's convention matches the source data.
The result converts energy only. It does not by itself determine power, operating time, fuel use, efficiency, or electricity cost.

Common questions

Is a food Calorie the same as the calorie option?

Usually, no. The capitalized Calorie used on food labels conventionally represents one kilocalorie, equal to 1,000 small calories. If a label reports 250 Calories, enter 250 kilocalories rather than 250 calories. The distinction matters because choosing calories would make the converted energy 1,000 times too small.

Can this convert kilowatts to BTU?

No, not without additional information. Kilowatts measure power, while the supported BTU and kWh selections measure energy. To obtain energy from kilowatts, first multiply the power by an operating duration, producing a value such as kWh. Likewise, BTU per hour is a power rate and is not the same quantity as BTU.

References and verification

The example and behavioral notes were checked against the browser implementation. Standards and primary references below define the relevant format, formula, or platform behavior.