Convert Calories to Kilojoules
Instantly convert Calories (cal) to Kilojoules (kJ) with our free online calculator.
Formula: cal to kJ — multiply by 0.004184
Reference Table
| Calories (cal) | Kilojoules (kJ) |
|---|---|
| 1 | 0.004184 |
| 5 | 0.02092 |
| 10 | 0.04184 |
| 25 | 0.1046 |
| 50 | 0.2092 |
| 100 | 0.4184 |
How to Convert Calories to Kilojoules
Formula
To convert Calories (cal) to Kilojoules (kJ): multiply by 0.004184
Step-by-Step
- Start with your value in Calories (cal).
- Multiply by 0.004184 to perform the conversion.
- The result is your value expressed in Kilojoules (kJ).
Conversion Factor
1 cal = 0.004184 kJ
Reverse Factor
1 kJ = 239.006 cal
Worked Example
Convert 25 Calories to Kilojoules: 25 cal = 0.1046 kJ
About Calorie (cal)
The 'small' gram-calorie (also called thermochemical calorie), defined as exactly 4.184 joules per ISO 31-4 / IUPAC convention — the energy needed to raise one gram of liquid water by 1 °C at standard conditions. This is the scientific calorie used throughout chemistry, physics, and biochemistry literature: enzyme kinetic data, calorimetric measurements (DSC instruments report energy in cal/g for melting transitions), Hess's law calculations, and the thermochemistry tables in the CRC Handbook all use cal. The gram-calorie is NOT the larger 'Calorie' (Cal, capital C) used on US food labels, which is actually a kilocalorie (1 Cal = 1 kcal = 1,000 gram-calories). The cal/Cal naming clash is a notorious source of confusion when cross-referencing nutrition data against scientific literature — a 'low-calorie' food labelled 'only 100 Calories' delivers 100,000 small calories. Two slightly-different historical 'calorie' definitions exist (thermochemical 4.184 J; 'International Table' or IT calorie 4.1868 J), with the thermochemical version dominant in modern usage.
About Kilojoule (kJ)
A metric unit of energy equal to exactly 1,000 joules. Kilojoules are the working unit for food-energy labelling outside the United States — Australia and New Zealand display kJ-only nutrition panels per FSANZ standards 1.2.7 / 1.2.8, the European Union requires kJ alongside kcal per EU Regulation 1169/2011, and Codex Alimentarius (the international food labelling standard) uses kJ. Reference values: a Big Mac is ~2,220 kJ, an adult daily energy intake is 8,000-10,500 kJ (about 2,000-2,500 kcal) per WHO/FAO Recommended Dietary Allowances, a 350 mL soft drink ~600 kJ. The kJ is also the natural engineering unit for small-scale mechanical work (joules per stroke on a punch press), small-cell battery capacity (e.g., a smartphone Li-ion at ~40 kJ), and small-scale thermodynamic calculations like an espresso machine's per-shot energy budget (~20 kJ). 1 kJ = 0.2389 kcal = 0.948 BTU = 277.8 mWh.
Quick Facts
- 1 Calorie equals 0.004184 Kilojoules
- 1 Kilojoule equals 239.006 Calories
- Calorie is a unit of energy
- Kilojoule is a unit of energy
- This conversion is commonly used in nutrition, electrical billing, physics, and mechanical engineering
- The Kilojoule belongs to the metric system
Common Calorie to Kilojoule Conversions
| Calories (cal) | Kilojoules (kJ) |
|---|---|
| 0.01 | 0.00004184 |
| 0.1 | 0.0004184 |
| 0.25 | 0.001046 |
| 0.5 | 0.002092 |
| 1 | 0.004184 |
| 2 | 0.008368 |
| 3 | 0.012552 |
| 5 | 0.02092 |
| 10 | 0.04184 |
| 15 | 0.06276 |
| 20 | 0.08368 |
| 25 | 0.1046 |
| 50 | 0.2092 |
| 75 | 0.3138 |
| 100 | 0.4184 |
| 250 | 1.046 |
| 500 | 2.092 |
| 1000 | 4.184 |
| 5000 | 20.92 |
| 10000 | 41.84 |
Understanding Calories
The Calorie (symbol: cal) is a unit of energy. The 'small' gram-calorie (also called thermochemical calorie), defined as exactly 4.184 joules per ISO 31-4 / IUPAC convention — the energy needed to raise one gram of liquid water by 1 °C at standard conditions. This is the scientific calorie used throughout chemistry, physics, and biochemistry literature: enzyme kinetic data, calorimetric measurements (DSC instruments report energy in cal/g for melting transitions), Hess's law calculations, and the thermochemistry tables in the CRC Handbook all use cal. The gram-calorie is NOT the larger 'Calorie' (Cal, capital C) used on US food labels, which is actually a kilocalorie (1 Cal = 1 kcal = 1,000 gram-calories). The cal/Cal naming clash is a notorious source of confusion when cross-referencing nutrition data against scientific literature — a 'low-calorie' food labelled 'only 100 Calories' delivers 100,000 small calories. Two slightly-different historical 'calorie' definitions exist (thermochemical 4.184 J; 'International Table' or IT calorie 4.1868 J), with the thermochemical version dominant in modern usage.
Calories are commonly used in nutrition, electrical billing, physics, and mechanical engineering.
Understanding Kilojoules
The Kilojoule (symbol: kJ) is a unit of energy. A metric unit of energy equal to exactly 1,000 joules. Kilojoules are the working unit for food-energy labelling outside the United States — Australia and New Zealand display kJ-only nutrition panels per FSANZ standards 1.2.7 / 1.2.8, the European Union requires kJ alongside kcal per EU Regulation 1169/2011, and Codex Alimentarius (the international food labelling standard) uses kJ. Reference values: a Big Mac is ~2,220 kJ, an adult daily energy intake is 8,000-10,500 kJ (about 2,000-2,500 kcal) per WHO/FAO Recommended Dietary Allowances, a 350 mL soft drink ~600 kJ. The kJ is also the natural engineering unit for small-scale mechanical work (joules per stroke on a punch press), small-cell battery capacity (e.g., a smartphone Li-ion at ~40 kJ), and small-scale thermodynamic calculations like an espresso machine's per-shot energy budget (~20 kJ). 1 kJ = 0.2389 kcal = 0.948 BTU = 277.8 mWh.
It belongs to the metric measurement system.
Kilojoules are commonly used in nutrition, electrical billing, physics, and mechanical engineering.
Why Convert Calories to Kilojoules?
Converting energy between Calories and Kilojoules is common in physics, nutrition, and engineering. Electricity bills use kilowatt-hours, food labels list calories or kilojoules, and mechanical engineers work with joules and BTUs. Reliable conversion helps professionals and consumers compare energy values across different contexts.
Frequently Asked Questions
How do I convert Calories to Kilojoules?
The 'small' gram-calorie (also called thermochemical calorie), defined as exactly 4. To convert Calories to Kilojoules, multiply by 0.004184. For example, 25 cal equals 0.1046 kJ.
How many Kilojoules are in 1 Calorie?
There are 0.004184 Kilojoules in 1 Calorie.
How many Calories are in 1 Kilojoule?
There are 239.006 Calories in 1 Kilojoule.
What is the formula for Calorie to Kilojoule conversion?
The formula is: multiply by 0.004184. This means 1 cal = 0.004184 kJ.
Is a Calorie bigger than a Kilojoule?
Yes. One Calorie is larger than one Kilojoule because 1 cal equals 0.004184 kJ, which is less than 1.
When do you need to convert between Calories and Kilojoules?
A metric unit of energy equal to exactly 1,000 joules. Calorie and Kilojoule are both energy units, so conversion comes up whenever one source of information uses one unit and another uses the other — a classic cross-reference challenge in engineering, trade, travel, and everyday life.