Energy Converter

This page converts an energy from one unit into another. Every value passes through the joule, the SI unit energy is held in, and energy stays energy: a unit only converts inside its own dimension.

How do you convert energy between joules, kilowatt-hours, calories and BTU?

Pick the unit you have, pick the unit you want, and type the value. The page multiplies by the factor between the two and prints the arithmetic under the result, so the answer and the working are the same object.

1. Choose the unit your value is in. This page opens on the kilowatt-hour.
2. Choose the unit you want it in. This page opens on the British thermal unit (International Table).
3. Type the value. The result and the factor behind it appear together.
4. Read the working. It converts into the joule first and out again, which is the same two lines you would write by hand.

Energy Conversion Table

One row per unit this page offers, each measured against the joule. The last column says whether the factor is a definition or a reading of one.

Worked Examples

The question the bank ranked highest for this page, answered with the working.

Where These Factors Come From

Every number above is read from the knowledge base rather than computed for the page. These are the statements it holds for energy.

• One joule is one newton metre, the work done moving one newton through one metre. One kilowatt-hour is exactly 3.6 MJ.
• Calorie and BTU each come in more than one size. The thermochemical calorie is exactly 4.184 J and the International Table calorie is exactly 4.1868 J; the International Table BTU is exactly 1055.05585262 J. A food Calorie is a kilocalorie.
• One electronvolt is exactly 1.602176634 x 10^-19 J, because the elementary charge has been an exact defined value since the SI was redefined in 2019.
• An exact factor is a definition rather than a measurement. 1 in = 25.4 mm and 1 lb = 0.45359237 kg were fixed by the 1959 international yard and pound agreement, so they never gain another digit.
• How this page reports a result result in the target energy unit; the calorie and BTU variants are named in full, never abbreviated to 'cal' or 'BTU' alone

SI prefixes on this page

Which Calorie and Which BTU?

The calorie comes in a thermochemical size and an International Table size, and so does the British thermal unit. This page names each variant in full rather than writing a bare cal or BTU, because a figure that does not say which one it means cannot be checked.

The rule behind this factor is the same for every unit - base units and derived units.

Frequently Asked Questions

Related Conversions

• Volumetric flow rate sits in the same measurement group as energy - read a flow rate in another unit.
• Power sits in the same measurement group as energy - power in watts, horsepower and BTU per hour.
• If you are measuring pressure rather than energy, force spread over an area instead.
• If you are measuring mass rather than energy, kilograms and pounds side by side instead.
• If you are measuring torque rather than energy, torque in newton-metres, pound-feet and kilogram-force metres instead.
• If you are measuring pace rather than energy, pace as the reciprocal of speed instead.

The rest of the family sits on all the unit converters.