Calories to Kilocalories Converter

The thousand that causes all the confusion

A kilocalorie is a thousand calories. That is the whole conversion — and it is also the reason nutrition figures are so often misquoted.

1 kcal = 1,000 cal

The Calorie printed on food packaging is a kilocalorie. Someone eating "2,000 calories a day" is eating 2,000 kcal, which is 2,000,000 small calories. The capital C is supposed to mark the difference, and is ignored almost universally.

In scientific writing the ambiguity is avoided by using joules, which is part of why SI prefers them.

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 kilocalorie

A thousand small calories, and what a food label means by "Calorie" or "Cal". A kilocalorie is 4,184 joules, or 4.184 kJ.

Nutrition labelling is where the ambiguity does most damage. When a packet says 250 Calories it means 250 kcal, which is 1,046 kJ. It does not mean 250 of the calories used in a chemistry class.

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.

• 100 cal to kcal
• 250 cal to kcal
• 500 cal to kcal
• 1,000 cal to kcal
• 1,500 cal to kcal
• 2,000 cal to kcal
• 2,500 cal to kcal
• 5,000 cal to kcal
• 10,000 cal to kcal
• 20,000 cal to kcal
• 50,000 cal to kcal
• 100,000 cal to kcal
• 250,000 cal to kcal
• 500,000 cal to kcal
• 1,000,000 cal to kcal

Quick reference

Calories	Kilocalories
100 cal	0.1 kcal
500 cal	0.5 kcal
1,000 cal	1 kcal
2,000 cal	2 kcal
5,000 cal	5 kcal
10,000 cal	10 kcal
100,000 cal	100 kcal
1,000,000 cal	1,000 kcal

Questions people ask

How many calories in a kilocalorie?

Exactly 1,000.

Is a kcal the same as a food Calorie?

Yes. The Calorie on a nutrition label is a kilocalorie.

Why do two units share a name?

Historical accident. The food industry adopted the kilocalorie and kept calling it a calorie, and the usage stuck.