Convert Calories to Joules – Energy Converter
This converter converts energy values between calories (small calorie, cal) and joules (J) using internationally accepted definitions. It also explains the dietary Calorie (capital C) which equals one kilocalorie (kcal).
The thermochemical calorie is the conventional reference for scientific work: 1 cal = 4.184 J. For food energy, the common label 'Calorie' (capital C) denotes 1 kilocalorie, equal to 1000 small calories or 4184 joules.
Interactive Converter
Convert between calorie and joule with precision rounding.
Quick reference table
| Calorie | Joule |
|---|---|
| 1 cal | 4.18 J |
| 5 cal | 20.92 J |
| 10 cal | 41.84 J |
| 25 cal | 104.6 J |
| 50 cal | 209.2 J |
| 100 cal | 418.4 J |
Methodology
We apply the fixed, internationally recognized conversion factor for the thermochemical calorie: 1 small calorie (cal) = 4.184 joules (J). This factor is used by national measurement institutes and referenced in SI and metrology documentation.
For dietary energy, values labeled with a capital 'Calorie' (Cal) are treated as kilocalories (kcal). The converter supports converting either cal → J or kcal → J by applying the appropriate scale factor (×1 or ×1000) before multiplying by 4.184.
Where precision matters (laboratory measurements, instrumentation reports, regulatory declarations), follow calibration and uncertainty guidance from national metrology institutes and accredited test laboratories (for example, NIST guidance and ISO/IEC 17025 practices).
Worked examples
100 cal → 100 × 4.184 = 418.4 J
1 kcal (1 dietary Calorie) → 1 × 4184 = 4184 J
250 kcal (typical food serving) → 250 × 4184 = 1,046,000 J (≈ 1.046 MJ)
Expert Q&A
Is a dietary 'Calorie' the same as a small calorie?
No. Food labels use the term Calorie (capital C) to mean kilocalorie (kcal). 1 Calorie (food) = 1 kcal = 1000 small calories (cal) = 4184 J.
Which definition of 'calorie' does this converter use?
This converter uses the thermochemical calorie definition commonly adopted in chemistry and reference sources: 1 cal = 4.184 J. Older or context-specific definitions exist historically, but they are uncommon in modern scientific practice.
How many significant figures should I use when converting?
Match the precision of the original measurement. For instrument-derived values, report the conversion with the same number of significant figures and include uncertainty if required. For example, if you measure 123.4 cal (four significant figures), convert and report with comparable precision: 123.4 × 4.184 = 516.8 J (rounded appropriately).
Can I convert food energy into joules for recipes or lab calorimetry?
Yes. For recipes and general use, convert dietary Calories (kcal) to joules using 1 kcal = 4184 J. For calorimetry or research, ensure instruments are calibrated and account for measurement uncertainty per NIST and ISO/IEC 17025 guidance.
Are there measurement or calibration considerations I should be aware of?
Yes. Converting units is exact given the defined factor, but your input value may have measurement error. For precise work, follow calibration schedules and uncertainty reporting recommended by national metrology institutes and accredited lab standards (for example, NIST and ISO/IEC 17025).
Sources & citations
- NIST — Reference on Units and Constants (Units and unit conversions) — https://physics.nist.gov/cuu/Units/units.html
- BIPM — The International System of Units (SI Brochure) — https://www.bipm.org/en/publications/si-brochure/
- USDA FoodData Central (food energy data and nutrient information) — https://fdc.nal.usda.gov/
- MIT OpenCourseWare (educational resources on energy units and conversions) — https://ocw.mit.edu/