Convert J to cal joules ↔ calories Free Online Secure
Type a value in joules and read it in calories at once. The factor is exact by definition, the arithmetic happens in your browser, and nothing is sent anywhere.
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Common values — Convert J to cal (joules ↔ calories)
| J | cal |
|---|---|
| 1 | 0.239005736138 |
| 2 | 0.478011472275 |
| 3 | 0.717017208413 |
| 5 | 1.19502868069 |
| 10 | 2.39005736138 |
| 20 | 4.78011472275 |
| 50 | 11.9502868069 |
| 100 | 23.9005736138 |
Where these units come from
Energy collected a unit from every field that discovered it separately. The joule is the SI one and the plainest: a newton acting over a metre. The calorie came from the study of heat and was defined by warming water one degree — which is why there are several of them, depending on which degree you start from; the thermochemical calorie, exactly 4.184 J, is the one used here. The kilowatt hour is not a physicist's unit at all but an accountant's: a kilowatt drawn for an hour, which is how electricity is sold. The BTU is its British cousin, built from the pound and the Fahrenheit degree, and it still runs the heating and cooling trade worldwide.
Where you meet them
Joules belong to physics and to food labels outside the English-speaking world. Kilowatt hours arrive on every electricity bill and describe the capacity of batteries, from a phone to a car. BTUs rate air conditioners, boilers and gas appliances almost everywhere, including in countries that are otherwise entirely metric. Calories — in practice kilocalories — rule nutrition, which is the one place where the unit's name is routinely a thousand times out.
Questions people ask
What is a joule in everyday terms?
A joule is about the energy needed to lift a small apple, around 100 grams, by one metre. It is also the energy of one watt flowing for one second, and one newton moving something one metre. It is a small unit, which is why household energy is counted in kilojoules, megajoules or kilowatt hours.
Is the calorie on a food label the same as the one here?
No, and the difference is a factor of a thousand. The Calorie printed on food is a kilocalorie: a thousand of the calories used on this page. A 500-Calorie meal is 500,000 calories in the physicist's sense, or about 2.1 megajoules. Food labels in most of the world now print kilojoules beside it, which avoids the ambiguity entirely.
Is the answer exact?
Where both units are defined in terms of one another by whole numbers, yes — the page says so above the figure, and the only rounding is in how many digits are shown. Where the ratio has no finite decimal, the page shows twelve significant digits and says the relation is approximate rather than pretending otherwise.
Does anything I type leave my device?
No. The arithmetic runs in your browser; nothing is uploaded and there is no server to upload it to. Load the page once and it keeps working with the network switched off.
Joules to calories: why a food label shows two numbers and a physics book a third
A packet of oat biscuits shows 1,550 kJ and 370 kcal side by side. A fitness tracker counts kilocalories, a chemistry book quotes calories per mole, and a physics book gives joules. All of them measure the same thing, energy, in units that differ by factors of 4.184 and 1,000. To convert J to cal for the small calorie, multiply by 0.23901: 100 J is 23.9 cal, 1,000 J is 239 cal and 4,184 J is exactly 1,000 cal. The calculator above multiplies as you type, and the sections below explain the whole unit family, from the thermochemical calorie to the "Calorie" on your breakfast cereal.
The page gives the rule with worked examples, a profile of each unit, a comparison and a long run of surprising comparisons between food, batteries and fuel, followed by the usual mistakes. The calculation runs in your browser and nothing you type is sent anywhere. Note that this page uses the small calorie, 4.184 J, not the kilocalorie of nutrition.
How to convert J to cal: multiply by 0.23901
The rule
The thermochemical calorie is defined as exactly 4.184 joules, so one joule is 1 / 4.184 = 0.239006 calories. To convert J to cal, multiply the joules by 0.23901: 50 J gives 11.95 cal, 400 J gives 95.6 cal and 10,000 J gives 2,390 cal. To go back, multiply calories by 4.184.
Worked examples
A banana of about 400 kJ holds 400,000 J, which is 95,600 cal or 95.6 kcal. A daily intake of 8,368 kJ is 2,000,000 cal, which is 2,000 kcal. A single joule, roughly the energy needed to lift a small apple by a metre, is 0.239 cal.
An exact factor
The value 4.184 J per calorie is a definition, so the factor carries no uncertainty. Other calories exist, such as the international table calorie of 4.1868 J, but they differ by less than 0.1 per cent.
A quick sanity test
The answer in calories is about four times smaller than the number of joules. If a “convert J to cal” calculation gave a larger number than you started with, you multiplied by 4.184 instead.
The joule
The SI unit of energy
The joule is the energy transferred when a force of one newton acts over one metre. It equals one watt-second, so a 100 W lamp uses 100 J every second. Food labels in Europe, Australia and many other countries give energy in kilojoules.
Where it appears
Physics, chemistry, electrical engineering and nutrition labels in kJ.
The calorie
The old unit of heat
The small calorie is the heat needed to warm one gram of water by one degree Celsius, fixed at 4.184 joules. The kilocalorie, a thousand times larger, is the "Calorie" of diet charts and the "kcal" on labels. Mixing the two is a common mistake.
Where it appears
Calorimetry, older textbooks, specific-heat tables and, as kcal, nutrition.
Joules against calories
One calorie is 4.184 J, so the figure in calories is nearly four times smaller. An energy of 1,000 J is 239 cal and one of 100,000 J is 23,901 cal. Both units measure the same energy; only the scale differs.
The conversion is exact. The only trap is the family: 1,000 cal make one kilocalorie, which is 4,184 J.
Where the conversion shows up
Food labels
A European label gives kJ and kcal, such as 1,550 kJ and 370 kcal for 100 g of oats. One kcal is 4.184 kJ, so 1,550 kJ is 370.5 kcal. In small calories the same amount is 370,500 cal. A “convert J to cal” calculation on a kJ value gives cal, and dividing by 1,000 gives kcal.
Batteries against biscuits
A phone battery of 15 Wh stores 54,000 J, which is 12,906 cal or 12.9 kcal. A 250 kcal chocolate bar holds as much energy as 116 AA cells of 2.5 Wh each. A “convert J to cal” calculation for the battery against the biscuit makes the comparison clear: a person can run for an hour on a snack.
Climbing a mountain
An 80 kg climber lifted from sea level to the top of Everest gains 6.94 MJ of potential energy, which is 1,660 kcal. Because muscles are only about 25 per cent efficient, the body spends around 6,600 kcal, 27.8 MJ, on the lifting alone.
Calories and Calories
In English "calorie" may mean the small calorie, 4.184 J, or the large Calorie, 4,184 J, also called the kilocalorie. On American food labels "Calories" with a capital C means kilocalories. A physics text that writes "cal" almost always means the small one, which is what this converter uses.
Cooling a coffee
A cup of 250 ml of coffee cooling from 90 °C to 60 °C loses 250 × 30 = 7,500 cal, 31.4 kJ. That is less than the 100 kJ in a small biscuit. The energy in a hot drink is tiny compared with the energy in its food.
A cricket ball in flight
A cricket ball of 160 g flying at 40 m/s has a kinetic energy of 128 J, 30.6 cal. The same ball dropped from a window 10 metres up reaches the ground with 15.7 J, 3.75 cal. Such small amounts show how much more food has than moving things.
A jump and a sprint
A 70 kg person who jumps half a metre in the air spends 343 J of mechanical energy, which is 82 cal. A sprinter of 80 kg at 10 m/s carries 4,000 J of kinetic energy, 956 cal. At sprint speeds the body wastes far more as heat than it keeps as motion.
Sunlight per square metre
On a clear day the sun delivers about 1,000 W to each square metre. That is 1,000 J each second, or 239 cal per second. In an hour it is 3.6 MJ, 860 kcal, about the energy of a large meal falling on a doormat.
One kilowatt-hour in food
One kilowatt-hour is 3.6 MJ, which is 860 kcal. A household that uses 10 kWh in a day consumes 8,600 kcal of electrical energy, enough for four adults. The comparison puts electricity use and food on the same scale.
Sugar cubes
A 4 g sugar cube holds about 68 kJ, 16 kcal, or 16,250 cal. A can of cola with about 35 g of sugar holds nearly nine cubes. The energy in sugar is the same per gram as in other carbohydrates, around 17 kJ.
The mental shortcut
To convert J to cal in your head, divide by 4 and add 4 per cent. For 1,000 J: 250 less 10 gives 240, close to 239. For 400 J: 100 less 4 gives 96, against 95.6. The method suits quick estimates.
Spreadsheet formulas
To convert J to cal in a spreadsheet, put the energy in joules in column A and type =A2/4.184 in column B. For the reverse, =B2*4.184. A column with =A2/4184 gives kcal as a cross-check against food labels.
Rounding and precision
Food labels round to the nearest 5 or 10 kcal, so 370 kcal may be 365 to 374 kcal. When you convert J to cal from such a label, two or three significant figures are right. A figure like 370,500 cal looks precise but is not.
Landmarks to memorise
1 J is 0.239 cal. 4.184 J is 1 cal. 10 J is 2.39 cal. 100 J is 23.9 cal. 1,000 J is 239 cal. 4,184 J is 1,000 cal. 41,840 J is 10,000 cal. Use these to convert J to cal by eye.
Typical foods in kJ and kcal
An apple of 100 g holds 218 kJ, 52 kcal. A slice of bread of 100 g, 1,109 kJ, 265 kcal. A 330 ml can of cola holds 582 kJ, 139 kcal. A hundred grams of milk chocolate carries 2,284 kJ, 546 kcal. A medium egg holds 293 kJ, 70 kcal.
Reference ladder
20 J is 4.78 cal. 250 J is 59.75 cal. 500 J is 119.5 cal. 2,257 J is 539.4 cal. 10,000 J is 2,390 cal. 20,000 J is 4,780 cal. 100,000 J is 23,901 cal. 1,000,000 J is 239,006 cal. A ladder like this makes checks quick.
Checking by reversing
To check a “convert J to cal” calculation result, multiply the answer by 4.184. If 1,000 J became 239 cal, then 239 times 4.184 gives back about 1,000. A second test is size: the calorie figure is about four times smaller.
Link to kWh and BTU
One joule is 2.78 × 10⁻⁷ kWh and 9.48 × 10⁻⁴ BTU. A million joules is 0.278 kWh, 948 BTU and 239,006 cal. For large amounts of energy the kWh and the BTU are more convenient than the joule or the calorie.
A worked example
A label says a 60 g cereal serving holds 900 kJ. In kcal that is 215, in small calories 215,100. With 125 ml of semi-skimmed milk at 250 kJ, the breakfast holds 1,150 kJ, 275 kcal. Without the conversion it is hard to compare it with a tracker that logs kcal.
Why labels use both units
European rules require energy in kJ and kcal side by side, because shoppers were used to kcal while the SI unit is the joule. Australia and some other countries show only kJ. Americans see only Calories. A traveller therefore meets all three systems.
The old definition of the calorie
The calorie was once defined as the heat to raise a gram of water from 14.5 to 15.5 °C. That value, 4.1855 J, differs a little from the thermochemical 4.184 J. For nutrition the difference is smaller than the uncertainty of food tables.
Specific heat
Water has a specific heat of 4.184 J/(g·K), which is 1 cal/(g·K) by the definition of the calorie. Aluminium has 0.897 J/(g·K), 0.214 cal/(g·K), and copper 0.385 J/(g·K), 0.092 cal/(g·K). That is why a metal pan heats faster than the water in it.
Fuels in calories per gram
Wood holds about 16 MJ/kg, 3.8 kcal per gram, petrol 44 MJ/kg, 10.5 kcal per gram, and hydrogen 120 MJ/kg, 28.7 kcal per gram. Old fuel tables in kcal per kilogram turn into MJ per kilogram by multiplying by 4.184 and dividing by 1,000.
Two routes to one answer
You can go from J to cal directly with 0.23901, or via kcal: divide by 4,184 and multiply by 1,000. If the results disagree, a digit was copied wrongly.
Heat in a hot-water bottle
A hot-water bottle with 1.5 litres at 70 °C cooling to 30 °C releases 1,500 × 40 = 60,000 cal, 251 kJ. That is about 60 kcal, the energy of a small apple, and it keeps a bed warm for hours because the loss is slow.
Chocolate beats TNT
TNT releases 4.184 MJ per kilogram, which is exactly 1,000 kcal per kilogram. Milk chocolate holds 5,460 kcal per kilogram, more than five times as much energy by weight. The difference is that food burns slowly in the body, while the explosive releases its energy in microseconds.
The kettle and the biscuit
A 3 kW kettle running for a minute uses 180 kJ, 43 kcal. One biscuit of 100 kJ holds 24 kcal. A cup of tea made with 200 ml of water heated from 20 to 100 °C takes 67 kJ, 16 kcal, less than a single biscuit, so brewing tea costs less energy than a snack with it.
Fat as a store of energy
One kilogram of body fat holds about 37 MJ, which is 8,843 kcal. The common rule of thumb that losing 1 kg needs a deficit of about 7,700 kcal, 32 MJ, allows for water and lean tissue. In small calories the figure is 8.8 million.
Fat, carbohydrate, protein and alcohol
The energy per gram is 37 kJ, 8.8 kcal, for fat, 17 kJ, 4 kcal, for carbohydrate and protein, and 29 kJ, 6.9 kcal, for alcohol. Labels round these to 9, 4, 4 and 7 kcal per gram. In small calories, fat gives 8,843 cal per gram, and a “convert J to cal” calculation shows the scale.
Daily needs
An adult needs about 2,000 to 2,500 kcal a day, which is 8.4 to 10.5 MJ. The resting metabolism of a typical adult is about 1,500 kcal, 6.3 MJ, a day. A marathon uses around 2,600 kcal, 10.9 MJ. Doctors use kcal, national food tables use kJ.
The brain's budget
The human brain uses about 20 W, which is 72,000 J an hour, or 17.2 kcal. Over a day that is about 413 kcal, nearly a fifth of the body's total at rest. The same energy in small calories is 413,000 cal.
Walking a kilometre
A walker uses about 50 kcal for each kilometre, which is 209 kJ, or 50,000 cal. At a pace of 5 km/h that is an average of 290 W. A 100 km walk costs about 5,000 kcal, roughly 0.6 kg of body fat, which is why long walks need steady eating.
Petrol against food
A litre of petrol holds about 34 MJ, 8,126 kcal. That is the energy of nearly 4 days of an adult's food. A car engine turns only about 25 to 30 per cent into motion, and the human body is in the same range, which is a coincidence of two different machines.
More values for convert J to cal
A longer list of conversions
If the value you need is not in the first list, these further conversions may be close enough to read off directly:
- 0.1 J = 0.0239006 cal
- 0.5 J = 0.119503 cal
- 3 J = 0.717017 cal
- 4 J = 0.956023 cal
- 7 J = 1.67304 cal
- 15 J = 3.58509 cal
- 20 J = 4.78011 cal
- 75 J = 17.9254 cal
- 200 J = 47.8011 cal
- 500 J = 119.503 cal
- 2,000 J = 478.011 cal
- 10,000 J = 2,390.06 cal
Common slips with a “convert J to cal” calculation
Multiplying by 4.184
From joules to calories the number falls. If 1,000 J became 4,184, you used the factor for the opposite direction.
Calorie and kilocalorie
The small calorie is 4.184 J and the kilocalorie 4,184 J. The "calorie" on a food label is the kilocalorie. Confusing them gives an error of a thousand.
Different calories
The thermochemical calorie of 4.184 J differs slightly from the international table calorie of 4.1868 J. For ordinary work the difference is negligible.
Short answers
How do I convert J to cal?
Multiply the joules by 0.23901.
How many calories is 1,000 J?
239 cal.
How many calories is 4,184 J?
Exactly 1,000 cal.
How many joules is one calorie?
4.184 J.
Does my number leave my device?
No, the calculation runs in your browser.
More pages and a wrap-up
For other energy conversions see Convert J to kWh, Convert kWh to cal, Convert cal to kWh, Convert km to mi, Convert mi to km, Convert °C to °F, Convert °F to °C, Convert pt to cups, Convert °Ré to °F. The reverse direction is Convert cal to J.
In short, a “convert J to cal” calculation comes down to multiplying by 0.23901 and writing the unit beside the answer. Your number is computed locally, with no account and no upload.