BTU to Joules Converter
A BTU is 1,055.05585262 joules, so BTU to joules is one multiplication: J = BTU x 1,055.05585262. That makes 10 BTU 10,550.5585262 J, 100 BTU 105,505.585262 J and 1,000 BTU 1,055,055.85262 J. The factor is the International Table BTU, the definition ISO 31-4 fixes at exactly 1,055.05585262 J, and it is the only BTU in the menu: the thermochemical BTU of about 1,054.35 J and the 39 degree Fahrenheit BTU of about 1,059.67 J differ in the fourth digit, and neither is what this page returns. The page opens with British thermal unit in the From box and Joule in the To box, ahead of whatever pair the converter last remembered, and it answers while you type to twelve significant digits. Under the headline the same energy appears in kilojoules, calories, kilocalories, watt hours and kilowatt hours at once, so 1 BTU reads 1.05505585262 kJ, 252.164400722 cal, 0.252164400722 kcal, 0.293071070172 Wh and 0.000293071070172 kWh on one screen. The swap button between the two boxes turns the page into a joules to BTU converter without a reload.
1 BTU in every energy unit
Common questions
- How many joules are in a BTU?
- 1,055.05585262 J, exactly, under the International Table definition this page converts with. It scales the way you would expect: 2 BTU is 2,110.11170524 J, 3 BTU is 3,165.16755786 J, 5 BTU is 5,275.2792631 J, 10 BTU is 10,550.5585262 J, 50 BTU is 52,752.792631 J, 100 BTU is 105,505.585262 J and 1,000 BTU is 1,055,055.85262 J. Half a BTU is 527.52792631 J and a million BTU is 1,055,055,852.62 J. Type any of those into the From box and the headline updates as you type.
- Which BTU is this, since the definitions disagree?
- The International Table BTU, fixed at exactly 1,055.05585262 J, which is the factor behind every figure on this page and the value most engineering tables print. The rival definitions differ in the fourth digit: the thermochemical BTU is about 1,054.35 J, the 59 degree Fahrenheit BTU about 1,054.80 J, the 60 degree Fahrenheit BTU about 1,054.68 J, the mean BTU about 1,055.87 J and the 39 degree Fahrenheit BTU about 1,059.67 J. End to end that spread is about half a percent, and International Table against thermochemical is about 0.07 percent. The converter carries one BTU row and it is the International Table one, so a figure on another definition has to be worked out separately.
- What is the formula for BTU to joules?
- J = BTU x 1,055.05585262 going this way, and BTU = J / 1,055.05585262 going back, so 1 J is 0.000947817120313 BTU, 500 J is 0.473908560157 BTU, 1,000 J is 0.947817120313 BTU and 100,000 J is 94.7817120313 BTU. A kilojoule is that same division on a round number: 1 kJ is 0.947817120313 BTU. The swap button between the two boxes sets the reverse direction up for you, and 1,055.05585262 J comes back as exactly 1 BTU.
- Worked example: how many joules is 12,000 BTU?
- 12,660,670.2314 J. The same 12,000 BTU reads 12,660.6702314 kJ, 3,516.85284207 Wh and 3.51685284207 kWh in the list underneath. One caution about where a number like that usually comes from: a 12,000 BTU figure printed on a label is normally a rate of BTU per hour rather than a quantity of energy, so the honest reading of this conversion is 12,660,670.2314 joules per hour, and the watt hour row is the one that lines up with a power figure.
- Why does the calorie row say 252.164400722 rather than 252?
- Because the calorie in this converter is the thermochemical calorie, exactly 4.184 J, and 1,055.05585262 divided by 4.184 is 252.164400722. The International Table BTU is itself built on the International Table calorie of 4.1868 J, and counted in those a BTU is about 251.996. That unit is not in the menu, so the cal and kcal rows here are thermochemical throughout: 1 BTU is 252.164400722 cal and 0.252164400722 kcal, and 100 BTU is 25,216.4400722 cal and 25.2164400722 kcal.
- How many BTU is a kilowatt hour?
- 3,412.14163313 BTU, because a kilowatt hour is 3,600,000 J and a BTU is 1,055.05585262 J. A watt hour is a thousandth of that, 3.41214163313 BTU. Going the other way, 1 BTU is 0.293071070172 Wh and 0.000293071070172 kWh, and 100,000 BTU is 29.3071070172 kWh. All of those rows are on the page at the same time, so the watt hour figure doubles as a check on the joule figure.
- How is the answer rounded and copied?
- The arithmetic runs on the number you typed and only the display is rounded, to twelve significant digits with trailing zeros dropped, which is why 1 BTU reads 1,055.05585262 J and not 1,055.056. Digits are grouped with commas for reading, and Copy result copies the plain figure without them so it pastes into a spreadsheet. Magnitudes below a millionth, or at a thousand trillion and above, switch to exponential form: turn on Show 1 more in the readout and 1 BTU also appears as 6.585141e21 eV. The From box takes digits, one decimal point, an optional minus sign and exponent notation, so 1e3 and 1,000 are read the same way, and anything else raises a message naming what you typed instead of printing a wrong number. An empty box reads Ready rather than zero.
- Why does the page open on BTU and joules when I last converted something else?
- Because a page that names a pair should show that pair. This one sets British thermal unit and Joule on arrival, ahead of whatever the converter last remembered, and it leaves the main unit converter alone: go back to the converter itself and it is still on the pair you left it on. The number you last typed does travel with you, since it is usually the one you are still working on. Nothing is uploaded either: the factors ship with the page, so the arithmetic happens in your browser with no account and no network connection once the page has loaded.
Conversion factors are the exact legal definitions where one exists. An inch is exactly 2.54 cm and a pound exactly 0.45359237 kg, so those conversions are exact rather than approximate. Temperature uses offsets rather than factors, and that is shown in the working.