Divide kilojoules by 4.184. That is the whole of it. 8,700 kJ is 2,079 calories, 1,200 kJ is 287, and 400 kJ is 96.
Most converters will tell you that much, several of them to three decimal places. None mentions that the figure you typed in was rounded before it reached the label, by more than those decimals are worth.
Converting kj to calories takes two seconds. Below is the converter, then a table of the values people actually look up, then the reason no two tools agree.
Kilojoules are the metric unit for the same energy a calorie measures, which is why they sit beside every calorie figure on this site. If you have never had to read one, start with what a kilojoule is.
8,700 kJ is 2,079 calories.
Divides by 4.184, the exact conversion. Food labels usually round it to 4.2, which would give 2,071. The gap is under half a percent and it does not matter for anything you are likely to do with it.
kJ to Calories Table: 8,700 kJ Down to 100 kJ
Find your row.
| Kilojoules | Calories (at 4.184) | Calories (at 4.2) |
|---|---|---|
| 8,700 kJ | 2,079 calories | 2,071 calories |
| 8,400 kJ | 2,008 calories | 2,000 calories |
| 7,000 kJ | 1,673 calories | 1,667 calories |
| 6,000 kJ | 1,434 calories | 1,429 calories |
| 5,000 kJ | 1,195 calories | 1,190 calories |
| 4,000 kJ | 956 calories | 952 calories |
| 3,000 kJ | 717 calories | 714 calories |
| 2,500 kJ | 598 calories | 595 calories |
| 2,000 kJ | 478 calories | 476 calories |
| 1,800 kJ | 430 calories | 429 calories |
| 1,500 kJ | 359 calories | 357 calories |
| 1,200 kJ | 287 calories | 286 calories |
| 1,000 kJ | 239 calories | 238 calories |
| 800 kJ | 191 calories | 190 calories |
| 500 kJ | 120 calories | 119 calories |
| 400 kJ | 96 calories | 95 calories |
| 100 kJ | 24 calories | 24 calories |
The two columns are the exact conversion and the rule of thumb. The largest disagreement anywhere in the table is 8 calories, in the top row, and by the bottom row the two agree exactly.
Look at 8,400. Divided by 4.2 it is exactly 2,000, which is the only reason 8,400 kJ circulates as the kilojoule version of the US reference day. The tidiness belongs to the factor, not to the food.
Every row was computed at 4.184 and rounded to the nearest whole calorie. The third column is there so you can see the size of the gap rather than take a claim about it on trust. For the energy in real portions rather than round numbers, see typical foods.
Calories to kJ Table: Going the Other Way
Same arithmetic, multiplying instead of dividing.
| Calories | Kilojoules (at 4.184) | Kilojoules (at 4.2) |
|---|---|---|
| 100 calories | 418 kJ | 420 kJ |
| 200 calories | 837 kJ | 840 kJ |
| 250 calories | 1,046 kJ | 1,050 kJ |
| 300 calories | 1,255 kJ | 1,260 kJ |
| 400 calories | 1,674 kJ | 1,680 kJ |
| 500 calories | 2,092 kJ | 2,100 kJ |
| 1,000 calories | 4,184 kJ | 4,200 kJ |
| 1,200 calories | 5,021 kJ | 5,040 kJ |
| 1,500 calories | 6,276 kJ | 6,300 kJ |
| 2,000 calories | 8,368 kJ | 8,400 kJ |
| 2,500 calories | 10,460 kJ | 10,500 kJ |
The 1,000 calorie row is the factor itself written out, which makes it a useful anchor. A thousand calories is 4,184 kJ because a calorie is 4.184 kJ.
The row people quote is 2,000. That is 8,368 kJ exactly, or 8,400 kJ if you used the rule of thumb, which is where the rounder figure in circulation comes from. It sits near Australia’s 8,700 kJ without matching it, and the two were never converted from each other.
The Number You Typed In Was Already Rounded
US labels must declare calories “to the nearest 5-calorie increment up to and including 50 calories, and 10-calorie increment above 50 calories” (21 CFR 101.9(c)(1)). A pack reading 250 calories was somewhere between 245 and 254 before anyone rounded it.
Put the two sources of error next to each other. Rounding to the nearest 10 moves a 250 calorie figure by up to 5 calories. Choosing 4.2 over 4.184 on the same item moves it by about 1. The difference every converter is quietly arguing about is the smaller of the two by a factor of five.
Go one step further back and it gets looser. Under 21 CFR 101.9(c)(1)(i) a manufacturer can reach that calorie figure five different ways: specific Atwater factors, the general 4, 4 and 9 calories per gram, adjusted general factors, food-specific factors accepted by the FDA, or bomb calorimetry with a correction for protein. Ball, Burch and Barnes (The Conversation, 2023) note that commercial figures generally come from Atwater factors rather than calorimetry, which is expensive, and that the method assumes ingredient composition stays consistent.
Then there is the legal tolerance. Under 21 CFR 101.9(g)(5) a food is misbranded if its actual calorie content runs more than 20 percent above the declared value. Twenty percent is the band the label has to stay inside. The conversion factor argument is 0.38 percent.
So the decimals are theatre. Round to whole calories and stop.
Where 4.184 Comes From, and Where 4.2 Comes From
Neither number is more correct than the other, because they are not the same kind of number.
4.184 is the thermochemical calorie. Frederick Rossini defined it in 1930 as 4.1833 joules, and in 1948, when electrical units changed, it was restated as exactly 4.184 joules so the quantity it represented would not shift. It is a definition rather than a measurement, which is why it carries no error bar. Two other calories exist alongside it: the International Table calorie at exactly 4.1868 joules and the 15 degree calorie at about 4.1855. Food work uses the thermochemical one.
4.2 is a rounding, kept because you can do it in your head. Eat For Health, an Australian government site, puts one calorie at 4.2 kilojoules, and FSANZ’s own Nutrition Panel Calculator guidance says energy is expressed in kilojoules “where one kilocalorie is equal to approximately 4.2 kilojoules”. No standard or regulation could be found that requires 4.2 on a label, and none is claimed here. Victoria’s Better Health Channel, also government, uses 4.184 instead.
On a European label neither factor is used, because the two figures were never converted from each other. Annex XIV of Regulation 1169/2011 gives each nutrient its own pair: protein and carbohydrate at 17 kJ and 4 kcal per gram, a ratio of 4.25; fat at 37 and 9, a ratio of 4.111; fiber at 8 and 2, a ratio of 4.0. No single constant converts kilojoules to calories on that panel.
This site is inconsistent about it too. The homepage tells you one calorie is about 4.2 kJ, then says 8,700 kJ comes to about 2,080 calories, which is the 4.184 answer. Divide 8,700 by 4.2 and you get 2,071. The tables above use 4.184 throughout, matching the converter, and the rule of thumb stays because it is the one you can run without a phone.
For a faster estimate still, take a quarter. Multiplying kilojoules by 0.24 runs about 0.4 percent high.
Why a Calorie on a Food Label Is Really a Kilocalorie
A widely used unit converter reports 5 kJ as 1,195 calories. It is not broken. It is answering a different question.
A small calorie is the heat needed to raise 1 gram of water by 1 degree Celsius. A large Calorie, written with a capital C, does the same for 1 kilogram, which makes it 1,000 small calories and identical to one kilocalorie. Food labels use the large one and mostly drop the capital.
The convention is old. It traces to Wilbur Atwater’s food energy work, an article in Century magazine in 1887 and Farmers’ Bulletin 23 in 1894, and the USDA food tables he built at the end of that century. It was settled long before the US had any reason to think about switching units.
The practical test takes a second. If a converter turns a food label figure into a number in the thousands, it gave you small calories. Divide by 1,000.
8,700 kJ and 2,000 Calories Are Label Reference Days, Not Targets
8,700 kJ is the most converted number on this page, and it was never about you.
In Australia, percentage daily intake on a pack is calculated against an average adult diet of 8,700 kJ, using the daily intake reference values in Standard 1.2.8. Showing that percentage is voluntary, and FSANZ suggests the wording “based on an average adult diet of 8700 kJ”. The word carrying the weight is average. It is a shared denominator, so percentages on two different packs mean the same thing.
The US label says it outright in its own footnote: “The % Daily Value tells you how much a nutrient in a serving of food contributes to a daily diet. 2,000 calories a day is used for general nutrition advice.”
You are converting at all because the two rulebooks differ. Australia and New Zealand require energy in kilojoules and treat kilocalories as optional, so plenty of packs show kJ alone, while US labels declare calories and may add kilojoules in brackets, which most do not.
The two reference days are not the same quantity and were never meant to be. 8,700 kJ is 2,079 calories, roughly 4 percent above the US figure, and they were set separately in different countries against different evidence.
Neither was calculated for a specific person. What actually moves an individual’s energy needs is covered in kJs and you, and the rest of the unit explainers sit in the food energy library.
FAQ
How many calories is 8700 kJ?
8,700 kJ is 2,079 calories using the exact conversion of 4.184, or 2,071 calories using the 4.2 rule of thumb. It is the average adult reference day behind percentage daily intake on Australian food labels, which makes it a denominator for a percentage column rather than a target for any particular person.
Do I divide kJ by 4.2 or 4.184?
Either. 4.184 is the thermochemical calorie, a defined constant, and 4.2 is the everyday rounding used across Australian consumer health material. They differ by 0.38 percent, which is smaller than the rounding already applied to the label figure you are converting.
Is a calorie the same as a kilocalorie on a food label?
Yes. The calorie on a food label is the large Calorie, equal to 1,000 small calories and identical to one kilocalorie. Some unit converters return small calories instead, which is why one will tell you 5 kJ is 1,195 calories. If the answer comes back in the thousands, divide by 1,000.
How many calories is 1200 kJ?
1,200 kJ is 287 calories at 4.184, or 286 calories at 4.2. Nearby values: 1,000 kJ is 239 calories, 1,500 kJ is 359, and 1,800 kJ is 430. The full table above runs from 8,700 kJ down to 100 kJ.
Why do two kJ to calorie converters give me different answers?
Three reasons stack up. They use different factors (4.184, 4.2, or the International Table calorie at 4.1868), they round differently, and some return small calories rather than food calories. All three differences together are still smaller than the rounding and estimation already inside the label figure.