How to use Energy Converter
- Enter the Value in the unit you have, for example 1.
- Choose Convert from, such as Kilowatt-hours (kWh).
- Choose Convert to, such as Megajoules (MJ).
- Leave Decimal places at 2, or pick another precision.
- The result, the joule row and any definition note update as you change the values.
Example: Energy Converter
Convert kilowatt-hours to megajoules.
Options
- Calories
- Thermochemical calories, International Table calories and food Calories are separate lines on the list, so the definition is never guessed from the word calorie.
- Decimal places
- Sets display rounding to 0, 2, 4, 6 or 8 places for a fractional result. A whole result ignores the setting and keeps every digit, and a small nonzero result is never printed as zero.
Supported inputs and limits
Where your input is processed
This tool processes your input in this browser. Your text and files are not uploaded to UseFreeTools. Check this tool's limits for anything it may save on your device.
Where each energy factor comes from
The unit list is written from published definitions rather than from rounded conversions. A thermochemical calorie is exactly 4.184 J, an International Table calorie is exactly 4.1868 J, a food Calorie is 4,184 J, an International Table BTU is exactly 1055.05585262 J, a thermochemical BTU is 1054.35026444 J, and a foot-pound force is 1.3558179483314004 J, which is the international foot times the standard pound force. Naming the definition on the page keeps a nutrition figure and a chemistry figure from being quietly treated as the same number.
NIST Special Publication 811, Appendix B.8: calorie, Btu and foot pound-force factors
Why the electronvolt is an exact factor
The electronvolt is defined as the energy one elementary charge gains over a potential difference of one volt, and the elementary charge has been fixed at exactly 1.602176634e-19 coulombs since the 2019 revision of the SI. That makes the joule factor a definition rather than a measurement, which is why no uncertainty is carried in the conversion.
NIST CODATA, fundamental physical constants: elementary charge
NIST Special Publication 811, Appendix B.8: electronvolt factor
Questions about Energy Converter
Is a food Calorie the same as a calorie?
A food Calorie, the capital C kind printed on nutrition labels, is a kilocalorie: 1,000 thermochemical calories, or 4,184 J. A plain small calorie in a chemistry problem is usually the thermochemical calorie of exactly 4.184 J.
Which calorie definition does the tool use?
It uses whichever one you select and names it on the result. Thermochemical calories, International Table calories and food Calories are three separate entries on the list rather than one entry called calorie.
Is a watt-hour the same as a watt?
No. A watt is a rate of energy use and a watt-hour is an amount of energy, so one watt running for one hour is exactly 3,600 J. Convert rates on the Power Converter page.
Why is an electronvolt result so small?
One electronvolt is exactly 1.602176634e-19 J, so the joule figure is a tiny fraction. The tool prints the full value rather than rounding it to zero.