1 kcal is equal to 4.184 kj.
The conversion from kilocalories (kcal) to kilojoules (kj) involves multiplying the amount in kcal by 4.184, because 1 kilocalorie is defined as exactly 4.184 kilojoules. This relationship comes from the energy needed to raise the temperature of water.
Conversion Tool
Result in kj:
Conversion Formula
The formula to convert kilocalories (kcal) to kilojoules (kj) is:
kj = kcal × 4.184
This works because 1 kilocalorie is the amount of energy needed to raise the temperature of 1 kilogram of water by 1 degree Celsius, which equals 4184 joules or 4.184 kilojoules.
Example:
- If you have 1 kcal, multiply 1 × 4.184 = 4.184 kj.
- For 5 kcal, 5 × 4.184 = 20.92 kj.
Conversion Example
- Convert 2.5 kcal to kj:
- Multiply 2.5 by 4.184.
- 2.5 × 4.184 = 10.46 kj.
- The result shows 2.5 kcal equals 10.46 kj.
- Convert 10 kcal to kj:
- 10 × 4.184 = 41.84 kj.
- Simply multiply the kcal value by 4.184; no extra steps needed.
- Convert 0.75 kcal to kj:
- 0.75 × 4.184 = 3.138 kj.
- This shows smaller kcal values convert proportionally.
- Convert 15 kcal to kj:
- Multiply 15 × 4.184.
- Result is 62.76 kj.
Conversion Chart
| kcal | kj |
|---|---|
| -24.0 | -100.416 |
| -20.0 | -83.680 |
| -15.0 | -62.760 |
| -10.0 | -41.840 |
| -5.0 | -20.920 |
| 0.0 | 0.000 |
| 5.0 | 20.920 |
| 10.0 | 41.840 |
| 15.0 | 62.760 |
| 20.0 | 83.680 |
| 26.0 | 108.784 |
The chart shows the kj values for kcal ranging from -24.0 to 26.0. You can find the kcal value on the left and see its kj equivalent on the right by multiplying by 4.184. This helps quickly estimate energy values without calculation.
Related Conversion Questions
- How many kilojoules are in 1 kcal exactly?
- What is the kj equivalent of 1 kcal for food energy?
- Why do I multiply 1 kcal by 4.184 to get kj?
- Is 1 kcal the same as 4.184 kj always?
- Can I convert 1 kcal to kj using a simple formula?
- What does 1 kcal equal in kj when measuring calories?
- How do you convert 1 kcal to kj correctly?
Conversion Definitions
kcal: Kilocalorie, often called a “Calorie” in food labels, measures energy content. It represents the energy needed to raise 1 kilogram of water by 1 degree Celsius. Kilocalories are used mostly in nutrition to quantify the energy in food and drinks.
kj: Kilojoule is a unit of energy in the International System of Units. One kj equals 1000 joules, measuring work or heat energy. Kilojoules are commonly used worldwide to express energy, especially in scientific contexts and food energy labeling outside some countries.
Conversion FAQs
Why is the factor 4.184 used to convert kcal to kj?
The factor 4.184 comes from the exact amount of energy in joules needed to raise 1 gram of water by 1 degree Celsius, which is 4.184 joules. Since 1 kcal equals 1000 calories, and 1 calorie equals 4.184 joules, multiplying kcal by 4.184 converts it to kj.
Can kcal values ever be negative, and what does that mean?
Negative kcal values can appear in calculations but don’t make physical sense in energy content of food. They could represent energy deficits or errors in measurement. In energy balance, negative values indicate energy expenditure exceeding intake, but food energy is always positive.
Are kj and kcal interchangeable units?
They both measure energy, but kj and kcal are different units. 1 kcal equals 4.184 kj, so they are related but not interchangeable without conversion. Choosing which unit to use depends on regional standards or scientific preference.
Is the conversion exact or approximate?
The conversion factor 4.184 is exact by definition in physics. So converting kcal to kj using this factor is precise and not an approximation. Small rounding may occur in practical calculations but the factor itself is fixed.
Does temperature affect the kcal to kj conversion?
No, the conversion factor 4.184 is constant regardless of temperature. It defines the energy unit itself, so converting kcal to kj remains the same under all conditions, without temperature influence.