Convert Kilocalories to Kilojoules – Energy Converter
This converter transforms energy values expressed in kilocalories (kcal) to kilojoules (kJ) using the internationally recognized thermochemical relationship so you can compare nutrition labels, laboratory results, and engineering data in SI units.
The tool follows SI-consistent practice: 1 kilocalorie (kcal) = 4.184 kilojoules (kJ). Guidance and references from national metrology and standards organizations are provided below for auditing, calibration, and interoperability.
Interactive Converter
Convert between kilocalorie and kilojoule with precision rounding.
Quick reference table
| Kilocalorie | Kilojoule |
|---|---|
| 1 kcal | 0.24 kJ |
| 5 kcal | 1.2 kJ |
| 10 kcal | 2.39 kJ |
| 25 kcal | 5.98 kJ |
| 50 kcal | 11.95 kJ |
| 100 kcal | 23.9 kJ |
Methodology
We apply the fixed thermochemical conversion factor defined in international metrology guidance: multiply kilocalories by 4.184 to obtain kilojoules. This factor originates from measured definitions of the calorie and is the value used for nutrition labeling and most scientific work.
Where multiple historical calorie definitions exist, we adopt the thermochemical calorie (1 cal = 4.184 J) to remain consistent with SI practice and major standards bodies. For traceability and regulatory contexts consult the cited authoritative sources.
Worked examples
1 kcal → 4.184 kJ
100 kcal → 418.4 kJ
250 kcal → 1046.0 kJ
500 kcal → 2092.0 kJ
Further resources
External guidance
Expert Q&A
What is the exact relationship between kcal and kJ?
The accepted thermochemical relationship is 1 kilocalorie (kcal) = 4.184 kilojoules (kJ). This is the SI-consistent value used for scientific, nutritional, and regulatory reporting.
Why do some sources show a slightly different factor (e.g., 4.1868)?
Multiple historical definitions of the calorie exist (mean calorie, 15 °C calorie, thermochemical calorie). For consistency with SI and national metrology institutes we use the thermochemical definition (1 cal = 4.184 J). Use alternate factors only if a specific historical definition is required and document which definition was used.
How many significant digits should I report?
Match the precision to your input data and instrument uncertainty. For nutrition labels, one decimal place for kJ (or integer kJ) is common. For laboratory measurements, round according to your measurement uncertainty and traceability to standards (see NIST and BIPM guidance).
Does this converter handle negative values or zero?
Yes. The mathematical relationship is linear and applies to zero and negative values in contexts where negative energy is meaningful (e.g., bookkeeping of energy flows). Ensure negative results are physically meaningful for your application.
Is this suitable for regulatory nutrition labeling?
This conversion provides the standard numeric transformation used in nutrition labeling. Always follow the specific regulatory agency rules for rounding and presentation (for example, the relevant national food authority) when preparing labels or official documentation.
How do I ensure accuracy and traceability?
Use calibrated measurement equipment, document instrument uncertainty, and reference a recognized standard (NIST/BIPM/ISO). For critical work preserve raw data, calculation records, and the chosen definition of the calorie.
Sources & citations
- NIST — The International System of Units (SI) and unit conversion guidance — https://www.nist.gov/pml/weights-and-measures
- BIPM — International Bureau of Weights and Measures, SI Units — https://www.bipm.org/en/publications/si-brochure
- FDA — Food Labeling & Nutrition (guidance on energy declaration and rounding) — https://www.fda.gov/food/food-labeling-nutrition
- ISO 80000-1 — Quantities and units (international standard on units of measurement) — https://www.iso.org/standard/30669.html
- MIT OpenCourseWare — Thermodynamics and energy units (educational reference) — https://ocw.mit.edu