Joules to Kilocalories
An instant joules-to-kilocalories converter, with the formula and a reference table below.
| Joules | Kilocalories |
|---|---|
| 1 J | 0.000239 kcal |
| 2 J | 0.000478 kcal |
| 3 J | 0.000717 kcal |
| 5 J | 0.001195 kcal |
| 10 J | 0.00239 kcal |
| 25 J | 0.005975 kcal |
| 50 J | 0.01195 kcal |
| 100 J | 0.023901 kcal |
How to use
- Enter a value in the Joules field.
- The Kilocalories figure appears immediately — no button to press.
- Typing in the Kilocalories field converts back to Joules the same way.
- Use the reference table for the values that come up most often.
Joules to Kilocalories formula
To convert joules to kilocalories, multiply by 0.000239005736.
kcal = J × 0.000239005736
Put another way, one joule is exactly 1/4,184 of a kilocalorie.
Why this factor: the joule and the kilocalorie are both defined against the joule, so dividing one definition by the other gives 0.000239005736 directly. Both definitions are set out in full below.
To go the other way, divide by 0.000239005736 — or use the Kilocalories to Joules converter, which is the same calculation reversed.
Worked example
Start with 500 J. Multiply by 0.000239005736 to get 0.119503 kcal.
500 J × 0.000239005736 = 0.119503 kcal
The converter above does this for any value you type, in either direction.
What is a joule?
The joule is the SI unit of energy — the work done by one newton acting over one meter.
Definition: Defined as 1 N·m, equivalently one watt-second. Named after James Prescott Joule.
Where it is used: All scientific energy calculations, food energy on European labels, and mechanical work.
What is a kilocalorie?
A kilocalorie is 1,000 calories, and is what food labeling calls a 'Calorie'.
Definition: Exactly 4,184 joules.
Where it is used: Nutrition and dietary energy in the US and much of the world, and metabolic measurements.
Worth knowing: Written with a capital C ('Calorie') or as 'kcal' on labels. This is the unit meant by everyday talk about counting calories.
Joules vs Kilocalories
The joule is an SI unit while the kilocalorie is a specialized unit. That is why the factor between them is not a round number: the two systems were defined independently and only later tied together by exact agreement.
Frequently asked questions
How many kilocalories are in a joule?
One joule equals 0.000239005736 kilocalories.
What is the formula to convert joules to kilocalories?
Multiply the number of joules by 0.000239005736. To reverse it, divide by 0.000239005736 instead.
How do I convert kilocalories back to joules?
Divide by 0.000239005736, which is the same as multiplying by 4184.
How many kilocalories are in 10 joules?
10 J works out to 0.00239 kcal.
Is there anything to watch out for with kilocalories?
Written with a capital C ('Calorie') or as 'kcal' on labels. This is the unit meant by everyday talk about counting calories.
How is the joule defined?
Defined as 1 N·m, equivalently one watt-second. Named after James Prescott Joule.