ucUnitCloudInternational unit matrix

Mistake guide

Confusing kcal and kJ

Kilocalories and kilojoules are roughly the same.

01Assumption

Kilocalories and kilojoules are roughly the same.

02Actually

1 kcal = 4.184 kJ, defined exactly via the thermochemical calorie. A value of 500 kcal equals 2092 kJ. The difference is more than fourfold.

03Why

Food packaging shows both units side by side because kJ is the SI-compliant figure while kcal is the familiar one. The factor 4.184 is hard to estimate mentally, so mistakes appear when converting between labels and apps.

04Check

If a value looks surprisingly large it is probably given in kJ. The factor for kcal to kJ is 4.184, for kJ to kcal about 0.239. Note also that 1 kcal = 1000 cal — the calorie on labels is always the kilocalorie.

Matching conversions

Kilocalorie to Kilojoulekcal → kJEnergyKilojoule to KilocaloriekJ → kcalEnergyKilocalorie to Joulekcal → JEnergyKilowatt-hour to KilocaloriekWh → kcalEnergy

Matching tables

TableEnergy units compared

Unit family: Energy

Sources

NIST Guide to SI Appendix BNIST conversion-factor method and non-SI factors.BIPM SI BrochureSI base units, prefixes and official SI context.
When not to use

Do not use as the sole basis for official, medical, safety-critical or contractual decisions.

Citation

Citation note: UnitCloud, mistake guide, sources reviewed: September 2026. Source basis: NIST Guide to SI Appendix B · BIPM SI Brochure.