Joules to Calories Converter

Common questions

How many calories is 1 joule?

0.239005736138 cal, because a calorie is 4.184 joules and the division does not come out even. It scales the way you would expect: 10 J is 2.39005736138 cal, 20 J is 4.78011472275 cal, 50 J is 11.9502868069 cal, 100 J is 23.9005736138 cal, 500 J is 119.502868069 cal and 1,000 J is 239.005736138 cal. The one round number in the pair runs the other way: 4,184 J is exactly 1,000 cal. Type any of these into the From box and the headline updates while you type.

Is this the small calorie or the food Calorie?

The small calorie, which the unit menu lists as Calorie (cal) and which is worth 4.184 J. The Calorie written with a capital C on a nutrition label is a thousand of those, so it is the Kilocalorie (kcal) row in the same list, worth 4,184 J. The gap is a factor of 1,000 and it is the reason this conversion gets misread: 1,000 J is 239.005736138 small calories and 0.239005736138 food Calories, and 1 J is 0.000239005736138 kcal. Both rows are printed under the answer at the same time, so you can read whichever one your source meant. If the number you have came off a food label, it is Calories with a capital C and the kcal row is the one to read; if it came from a physics problem or a datasheet, it is almost always the small calorie.

What is the formula, and is the 4.184 factor exact?

cal = J / 4.184 going this way, and J = cal x 4.184 going back. The factor is exact by definition rather than measured: the thermochemical calorie is defined as exactly 4.184 joules, and the kilocalorie as exactly 4,184 joules. So 1 cal is 4.184 J, 10 cal is 41.84 J, 100 cal is 418.4 J and 1,000 cal is 4,184 J, all exactly. The only rounding on this page is in the printing: an answer like 0.239005736138 cal is 1 / 4.184 cut to twelve significant digits, not an approximation of the factor.

Why do some tables say a calorie is 4.1868 joules?

Because more than one calorie was defined. This converter uses the thermochemical calorie, 4.184 J exactly, which is also the value behind the kilocalorie on nutrition labels. The International Steam Table calorie is 4.1868 J exactly, and the 15 degree Celsius calorie is about 4.1855 J. The three differ by less than a tenth of a percent: 4.1868 against 4.184 is about 0.067 percent, so 1,000 J is 239.005736138 thermochemical calories and 238.845896627 IT calories. The IT calorie is not one of the units in the menu, so if your source needs it, divide the joules by 4.1868 yourself rather than reading the cal row here.

How is the result rounded?

The conversion is done on the number you typed and only the display is rounded, to twelve significant digits with trailing zeros dropped, which is why 1 J reads 0.239005736138 rather than 0.239. Digits are grouped for reading, so 1,000,000 J shows as 239,005.736138 cal, and Copy result copies the figure without those commas so it pastes straight into a spreadsheet. Very large and very small magnitudes switch to exponential instead of a run of zeroes: with the uncommon units shown, 1 J reads 6.241509e18 eV. The From box takes digits, one decimal point, an optional minus sign and exponent notation, so 1e6 and 1,000,000 are both accepted, and anything else raises a message naming what you typed instead of printing a wrong number.

How do I convert calories back to joules?

Press the swap button between the two boxes and the pair reverses to calories into joules, or multiply by 4.184 yourself. One calorie is 4.184 J, 100 cal is 418.4 J, 239.005736138 cal is 1,000 J and 1,000 cal is 4,184 J. For food Calories choose Kilocalorie (kcal) in the From box first: 100 kcal is 418,400 J, which is 418.4 kJ, and 2,000 kcal is 8,368,000 J, which is 8,368 kJ.

What else is shown beside the calorie figure?

The whole energy category for the amount you typed, because the converter works out every unit at once rather than one target at a time. For 1,000 J that is 1 kJ, 239.005736138 cal, 0.239005736138 kcal, 0.277777777778 Wh, 0.000277777777778 kWh and 0.947817120313 BTU. Two of those are handy checks on the calorie figure: 1 Wh is 3,600 J and 860.420650096 cal, and 1 BTU is 1,055.05585262 J and 252.164400722 cal. The electronvolt is hidden until you turn on Show 1 more in the readout, since it is only useful at atomic scale.

Why does the page open on joules and calories when I last converted something else?

Because a page that names a pair should show that pair. This one sets joules in the From box and calories in the To box on arrival, ahead of whatever the converter last remembered, and it leaves the main unit converter alone: go back to /unit-converter and it is still on the pair you left it on. The amount you last typed does come with you, since it is usually the one you are still working on, and Start over at the top of the page clears it. Nothing you type is uploaded: the factors ship with the page, so the arithmetic happens in your browser.