Calories to Kj
Convert any value from kilocalorie to kilojoule with full precision. Use the converter above for instant results, or read on for the exact formula, worked examples, common uses, and answers to frequently asked questions.
About the Kilocalorie to Kilojoule conversion
Energy appears in many different units depending on the field. Physics uses joules, nutrition uses calories and kilocalories, electricity uses kilowatt-hours, heating and air-conditioning use BTU (British Thermal Units), and particle physics uses electronvolts. Converting between them correctly is essential in science, engineering, and everyday life.
This page focuses specifically on converting kilocalorie to kilojoule. Use the converter above for instant results, or read on for what each unit is, the exact formula, a worked example, and answers to common questions.
Understanding kilocalorie and kilojoule
What is a kilojoule?
The kilojoule equals 1,000 joules. It is used on food labels in many countries and for expressing moderate amounts of energy in science.
How a kilocalorie compares to a kilojoule
The kilocalorie is the larger of the two units: one kilocalorie is about 4.184 kilojoule. Because the kilojoule is smaller, the same length or quantity works out to a larger number when you measure it with that unit. Knowing which unit is larger is a quick way to sanity-check a conversion: if the numbers move in the wrong direction, the two units have probably been swapped.
Conversion formula
The exact mathematical relationship between kilocalorie and kilojoule is:
1 kilocalorie = 4.184 kilojoule
So to convert a value V from kilocalorie to kilojoule, use:
Vkilojoule = Vkilocalorie × 4.184
To go in the opposite direction:
Vkilocalorie = Vkilojoule × 0.23900574
These factors come from the international definitions published by NIST, BIPM, and ISO 80000 and are exact within their respective standard systems. The converter applies them with full floating-point precision.
Worked example
Using the formula above, here are some common values converted from Kilocalorie to Kilojoule:
| Kilocalorie | Kilojoule |
|---|---|
| 1 | 4.184 |
| 5 | 20.92 |
| 10 | 41.84 |
| 25 | 104.6 |
| 50 | 209.2 |
| 100 | 418.4 |
Sources and accuracy
The joule is the SI unit of energy, defined as the work done by a force of one newton over one meter (BIPM, NIST). One calorie equals exactly 4.184 joules by international definition. One BTU equals exactly 1055.05585262 joules. One electronvolt equals exactly 1.602176634×10⁻¹⁹ joules (since the 2019 SI redefinition).
Conversion factors are cross-checked against the NIST SP 811 guide, the BIPM SI brochure, and ISO 80000, plus published historical references for older unit systems. For mission-critical work such as medical dosing, legal-for-trade measurement, aerospace, or large-scale engineering, always verify independently with the original source.
Practical tips
When reading food labels, "calories" almost always means kilocalories (1 kcal = 1,000 cal = 4,184 J). When sizing air conditioners, one "ton" of cooling equals 12,000 BTU per hour.
Frequently asked questions
How many kilojoule are in one kilocalorie?
One kilocalorie equals 4.184 kilojoule. To convert, multiply your kilocalorie value by 4.184.
Which is bigger, a kilocalorie or a kilojoule?
The kilocalorie is bigger. One kilocalorie equals about 4.184 kilojoule.
How accurate is this kilocalorie to kilojoule converter?
It uses the official international conversion factors from NIST and BIPM with full double-precision floating-point accuracy. For everyday use the result is precise to many more decimal places than any practical measurement requires.
Can I convert kilojoule back to kilocalorie as well?
Yes. Use the swap button above to reverse the From and To fields, or change either dropdown to any unit in the energy category. The calculation runs entirely in your browser, so it also works offline once the page has loaded.