How many kJ are in 100 calories?

If they are food Calories (kcal), 100 × 4.184 = 418.4 kJ. If they are small calories (cal), it is only 0.4184 kJ.

How many kJ is 1 calorie?

A food Calorie (kcal) is 4.184 kJ. A small calorie (cal) is 0.004184 kJ.

How do I convert kJ to calories?

Divide by 4.184. 1,000 kJ is 239.0 kcal. Press the swap button to do it on this page.

Is 2,000 calories the same as 8,400 kJ?

Close, not exact. 2,000 kcal is 8,368 kJ. The EU reference intake of 8,400 kJ is rounded.

Why do some labels show both kJ and kcal?

Different countries ask for different units, and the European Union asks for both. Each figure is calculated from the food and rounded, so they may not match 4.184 exactly.

Are calories and kilocalories the same thing on a menu?

On food and fitness labels, yes: calories means kilocalories. In physics and chemistry a calorie is 1,000 times smaller.

Calories to Kilojoules (kcal to kJ) Converter

Common energy amounts in calories and kJ. Values are rounded to 4 decimal places.
Number of calories	kJ if kcal (food Calories)	kJ if cal (small calories)
1	4.184	0.0042
10	41.84	0.0418
50	209.2	0.2092
100	418.4	0.4184
150	627.6	0.6276
200	836.8	0.8368
250	1,046	1.046
300	1,255.2	1.2552
500	2,092	2.092
1,000	4,184	4.184
2,000	8,368	8.368
2,500	10,460	10.46

Number of calories

kJ if kcal (food Calories)

kJ if cal (small calories)

4.184

0.0042

41.84

0.0418

209.2

0.2092

100

418.4

0.4184

150

627.6

0.6276

200

836.8

0.8368

250

1,046

1.046

300

1,255.2

1.2552

500

2,092

2.092

1,000

4,184

4.184

2,000

8,368

8.368

2,500

10,460

10.46

At a glance

Formula

kJ = kcal × 4.184, where kcal is the food Calorie

Which calorie

The page opens on the food Calorie (kcal). The small calorie (cal) is 1,000 times smaller and is always shown beside it.

Examples

100 kcal = 418.4 kJ, 250 kcal = 1,046 kJ, 2,000 kcal = 8,368 kJ.

Back again

kcal = kJ ÷ 4.184. 1,000 kJ is 239.0 kcal.

Quick estimate

Multiply by 4.2. It is about 0.4% high.

Price

Free, no sign-up. Runs in your browser.

How to do it

Enter the number

Type it in Value. The box starts at 250.

Choose the calorie

Food Calorie (kcal) is the one on food labels and fitness trackers. Choose Small calorie (cal) only for physics or chemistry.

Read the kilojoules

The big number is for your choice. Underneath, both kinds of calorie are shown side by side so you can see the 1,000 times difference.

Go the other way

Press the swap button to turn kilojoules into calories, which is the sum for a label that lists only kJ.

Which calorie do you mean?

Nutrition uses a calorie that is not the one in the science textbook. The Calorie on a food label (sometimes written with a capital C, Cal, or as kcal) is a kilocalorie, which is 1,000 small calories. Its exact size is 4.184 kilojoules. The small calorie, the lowercase cal, is 4.184 joules, so 0.004184 kJ.

If you are converting something you read on a packet, a menu, a fitness tracker or a diet plan, you want the first one. A figure like 250 cal in a physics problem is a quarter of a kilocalorie, which is only about 1 kJ. This page keeps the two apart and shows both answers so a mistake cannot hide.

The formula, with examples

To convert food Calories to kilojoules, multiply by 4.184. To convert kilojoules to Calories, divide by 4.184, which is the same as multiplying by 0.239.

100 kcal is 100 × 4.184 = 418.4 kJ.
250 kcal is 1,046 kJ and 500 kcal is 2,092 kJ.
2,000 kcal, a common daily reference, is 8,368 kJ.
1,000 kJ is 1,000 ÷ 4.184 = 239.0 kcal.

For a quick estimate, multiply by 4.2. That is 0.38% higher than the exact factor, which is fine when you are comparing snacks. The table under the converter gives values from 1 to 2,500 for both kinds of calorie.

Why labels show kilojoules, calories or both

Labels in the United States list Calories only. In the European Union energy is listed in both kilojoules and kilocalories, and in Australia and New Zealand it is listed in kilojoules. The EU reference intake for an average adult is 8,400 kJ or 2,000 kcal. Those two numbers are not an exact conversion, since 2,000 kcal is 8,368 kJ. Labels work out kJ and kcal from the food's nutrients and round each one, so the pair on a packet can be a few units off the exact 4.184 ratio. Use the formula for your own sums and treat the label as the label.

Which factor, 4.184 or 4.1868?

This page uses the thermochemical calorie, 4.184 J, which is the factor used for food energy. The International Table calorie is 4.1868 J, about 0.07% larger, and appears in engineering and steam tables. For 100 kcal the difference is 418.4 kJ against 418.68 kJ. If you need the IT calorie, it is in the energy converter as calorie (IT).

Convert calories to kilojoules