Kilocalories and kilojoules
A kilocalorie is 1,000 calories, exactly 4,184 joules: the food Calorie. Nutrition labels, diet apps and fitness trackers count energy in kcal.
A kilojoule is 1,000 joules. Food energy in Australia, New Zealand and the EU is labeled in kilojoules alongside kilocalories.
Worked example
Convert 250 kcal: 250 × 4.184 = 1,046, so 250 kilocalories is 1,046 kilojoules. Likewise 100 kcal = 418.4 kJ.
Estimating in your head
Multiply by 4.2 for a quick figure; it is off by about 0.4%. For 250 kcal that gives 1,050 kJ, against 1,046 exactly.
Going the other way
To convert kilojoules to kilocalories, divide by 4.184 (or multiply by 0.239005736138). The swap button between the boxes opens that page.
How this works
kJ = kcal × 4.184
1 kcal = 4,184 J and 1 kJ = 1,000 J, both by definition, so the factor is their ratio: 4.184 exactly. Results drop binary floating-point noise beyond 15 significant digits and display at the precision you choose (6 significant figures by default). Copy result copies the full value.
Frequently asked
How many kilojoules are in a kilocalorie?
1 kilocalorie = 4.184 kilojoules, exactly. The value follows from the unit definitions, so it never changes.
How do I convert kilocalories to kilojoules?
Multiply by 4.184. For example, 100 kcal × 4.184 = 418.4 kJ.
What is 1,000 kcal in kilojoules?
1,000 kcal = 4,184 kJ. The table next to the converter lists more common values.
Is the result rounded?
Only on screen. The page computes with the exact definitions and removes floating-point noise past 15 significant digits; pick 3 to 12 significant figures, or use Copy result for the full value.
Sources
- NIST SP 811 Appendix B.8 — Factors for units listed alphabetically
- BIPM — The International System of Units (SI Brochure), 9th edition
- Wikipedia — Calorie
Reviewed Oct 17, 2026 · test vectors fixtures/units/energy/kcal-to-kj/