Joules to Calories Converter

Divide by 4.184 — or by 4,184

Which divisor you want depends on which calorie you mean. The scientific calorie is 4.184 joules; the Calorie on a food label is a thousand times bigger.

cal = J ÷ 4.184     Calories = J ÷ 4,184

If a result looks a thousand times off, the wrong calorie was used. That is almost always the explanation.

For food energy, the quick route from kilojoules is to divide by 4.184: a 1,000 kJ meal is 239 Calories.

The joule

The SI unit of energy: the work done when a force of one newton moves something one metre. It is a small unit — lifting an apple a metre off the table takes about one joule.

Everything else on this page is the same quantity counted differently. A joule is also one watt for one second, which is the link between energy and power.

The calorie

Originally the energy needed to raise one gram of water by one degree Celsius. The version used in chemistry — the thermochemical calorie — is now defined as exactly 4.184 joules.

The trap is that calorie means two different things. This small calorie is a scientific unit. The Calorie on a food label, usually written with a capital C, is a kilocalorie: a thousand of these. A 1,000-Calorie meal is 1,000,000 small calories.

The working, step by step

Every line updates with whatever you type above. The point is the method, which is the same for any pair of units in this family.

Copy the working

The same quantity, two different numbers

One physical amount, read off two scales. The tick marks do not line up, and the gap between them is the conversion factor made visible.

How much is that?

A number is easier to judge next to something familiar.

Your turn

Reading a method and being able to use it are different things. Answer within half a per cent and it counts as correct.

How to use this converter

1. Type into either box. The other side updates as you go; there is no button to press.
2. Swap the direction with the button between the boxes, carrying your value across.
3. Set the decimals if the default is more or less precision than you need.
4. Copy the answer with its unit, ready to paste.
5. Use the shortcut buttons for the values that come up most often.
6. Share the result. The address bar tracks what you type, so the link you copy opens on the same number.

Common uses and tips

Where this comes up

• Food labels. Europe and Australia print kilojoules; the United States prints Calories. The same packet often carries both.
• Nutrition and exercise tracking, where one app reports kJ and another kcal.
• Chemistry and physics coursework, where reaction enthalpies come in kJ/mol and older texts use calories.
• Physics at atomic scale, where electronvolts are the only sensible size.

The trap: calorie and Calorie

The word means two things a thousand apart.

• calorie (small c) — the scientific unit, exactly 4.184 joules. Enough to warm a gram of water by one degree.
• Calorie (capital C), or kcal — a thousand of those, 4,184 joules. This is what every food label means.

So a 2,000-Calorie daily intake is 2,000 kcal, which is 2,000,000 small calories, or 8.37 megajoules. If a conversion comes out a thousand away from what you expected, this is why.

Tips worth knowing

• 4.184 is the number to remember. It works at every scale: cal to J, kcal to kJ, Mcal to MJ.
• Energy is not power. Joules are an amount; watts are a rate. They cannot be converted without a time.
• A kilowatt-hour is energy, not power: 3.6 MJ, or 860 kcal.

Values people look up most

Each one opens the converter with the number already in it.

• 1 J to cal
• 10 J to cal
• 100 J to cal
• 500 J to cal
• 1,000 J to cal
• 2,000 J to cal
• 4,184 J to cal
• 5,000 J to cal
• 10,000 J to cal
• 50,000 J to cal
• 100,000 J to cal
• 500,000 J to cal
• 1,000,000 J to cal
• 4,184,000 J to cal

Quick reference

Using the small calorie of 4.184 J.

Joules	Calories
1 J	0.239006 cal
10 J	2.390057 cal
100 J	23.900574 cal
1,000 J	239.005736 cal
4,184 J	1,000 cal
10,000 J	2,390.057361 cal
100,000 J	23,900.573614 cal
1,000,000 J	239,005.736138 cal

Questions people ask

How many calories in a joule?

0.239 small calories, or 0.000239 food Calories.

How do I convert kJ to Calories?

Divide by 4.184. A 1,000 kJ meal is 239 Calories.

Why do European labels show kJ and kcal?

Because EU rules require energy in kilojoules, and kilocalories are what most shoppers recognise.