# Kilocalories to kilojoules converter

> Convert kilocalories to kilojoules (kcal to kJ) with the exact factor, a conversion chart and worked steps.

Interactive version: https://www.calcopenly.com/conversion/kcal-to-kj
Subject: Unit converters

Nutrition labels often use Calories to mean kilocalories. Converting the stated energy into kilojoules allows comparison with another label's energy column. Check that both amounts refer to the same serving size; a per-serving figure is not a per-100-gram figure.

One kilocalorie is exactly 4.184 kilojoules, so 2000 kcal is 8,368 kJ. To convert kcal to kJ, multiply by 4.184; to convert back, multiply by 0.2390057361.

The kilocalorie used on food labels is the thermochemical kilocalorie, exactly 4.184 kJ. Because both units are defined exactly, the factor above is exact and the results here carry no conversion error.

## Inputs

- **Kilocalories (kcal)**

## Results

- Kilojoules (kJ) — main result
- Conversion
- 1 kJ in kilocalories (kcal)

## Formula

$$
\text{kilojoules} = \text{kilocalories} \times 4.184
$$

## Worked examples

### 2000 kcal to kJ

- Kilocalories (kcal): 2000 kcal
- **Kilojoules: 8,368 kJ**
- Checked against: Exact-fraction computation from the legal unit definitions (scripts/gen-pairs.py, Python fractions)

### 250 kcal to kJ

- Kilocalories (kcal): 250 kcal
- **Kilojoules: 1,046 kJ**
- Checked against: Exact-fraction computation from the legal unit definitions (scripts/gen-pairs.py, Python fractions)

### 50 kcal to kJ

- Kilocalories (kcal): 50 kcal
- **Kilojoules: 209.2 kJ**
- Checked against: Exact-fraction computation from the legal unit definitions (scripts/gen-pairs.py, Python fractions)

## Questions

### When would I convert kcal to kJ?

Nutrition labels often use Calories to mean kilocalories. Converting the stated energy into kilojoules allows comparison with another label's energy column. Check that both amounts refer to the same serving size; a per-serving figure is not a per-100-gram figure.

### How many kilojoules are in a kilocalorie?

One kilocalorie is exactly 4.184 kilojoules. The kilocalorie used on food labels is the thermochemical kilocalorie, exactly 4.184 kJ.

### How do you convert kcal to kJ?

Multiply the number of kilocalories by 4.184. For example, 2000 kcal × 4.184 = 8,368 kJ. To go the other way, divide by 4.184.

### How can I estimate kcal to kJ without a calculator?

Multiply by 4.2. That is 0.4% high of the exact factor 4.184, so 2000 kcal comes out as 8,400 kJ instead of 8,368.

### How accurate is the kilocalories to kilojoules converter?

Accuracy depends on your inputs and the method's assumptions. Decimal arithmetic uses 50 significant digits, but estimates, numerical methods and source data can be less precise; the displayed rounding does not remove those limits. It is checked against 3 worked examples whose answers come from independent sources; for example, “2000 kcal to kJ” is checked against Exact-fraction computation from the legal unit definitions (scripts/gen-pairs.py, Python fractions).

### Where does the method come from?

NIST SP 811 (2008), Guide for the Use of the International System of Units, Appendix B; NIST Handbook 44, Appendix C: General tables of units of measurement; BIPM, The International System of Units (SI Brochure), 9th edition.

## Sources

- [NIST SP 811 (2008), Guide for the Use of the International System of Units, Appendix B](https://www.nist.gov/pml/special-publication-811)
- [NIST Handbook 44, Appendix C: General tables of units of measurement](https://www.nist.gov/pml/weights-and-measures/publications/nist-handbooks/handbook-44)
- [BIPM, The International System of Units (SI Brochure), 9th edition](https://www.bipm.org/en/publications/si-brochure)