mmHg to Atm Converter
The conventional millimetre of mercury is a millimetre of mercury at 13,595.1 kg/m³ under a gravity of 9.80665 m/s², which works out to exactly 133.322387415 pascals, and a standard atmosphere is exactly 101,325 pascals. So mmHg to atm is one multiplication: atm = mmHg × 133.322387415 / 101,325, a division by 759.999891726 to twelve digits. That makes 1 mmHg 0.00131578966114 atm, 100 mmHg 0.131578966114 atm, 500 mmHg 0.65789483057 atm, 700 mmHg 0.921052762798 atm and 760 mmHg 1.00000014247 atm, which is just over 1 rather than exactly 1 because a torr and a conventional mmHg are not quite the same size. This page opens the converter with mmHg in the From box and atmospheres in the To box, whatever pair you converted last, and the list under the answer carries the same pressure in pascals, kilopascals, bar and pounds per square inch. It changes the units on a number and nothing else: a converted figure is still just a quantity, and what it means in a given setting is not something arithmetic can tell you.
1 mmHg in every pressure unit
Common questions
- How many atm is 1 mmHg?
- 0.00131578966114 atm, which is 133.322387415 / 101,325. It scales straight up: 10 mmHg is 0.0131578966114 atm, 100 mmHg is 0.131578966114 atm, 500 mmHg is 0.65789483057 atm, 750 mmHg is 0.986842245855 atm and 760 mmHg is 1.00000014247 atm. Answers print to twelve significant digits, and anything below 0.000001 switches to exponential notation, so 0.0001 mmHg reads 1.31579e-7 atm rather than a row of zeroes.
- What is the formula for mmHg to atm?
- Atmospheres = millimetres of mercury × 133.322387415 / 101,325, and millimetres of mercury = atmospheres × 759.999891726 going back the other way. Both constants are definitions rather than measurements: the 10th General Conference on Weights and Measures fixed one standard atmosphere at exactly 101,325 Pa in 1954, and the conventional mmHg is fixed at exactly 133.322387415 Pa by the mercury density and gravity written into it. The Swap units button between the two boxes reverses the pair, so this page becomes an atm to mmHg converter without a reload.
- Why is 760 mmHg not exactly 1 atm?
- Because 760 to the atmosphere is the definition of the torr, not of the millimetre of mercury. A torr is exactly 101,325 / 760 = 133.322368421 Pa. The conventional mmHg used here is 133.322387415 Pa, larger by about fourteen parts in a hundred million, so 760 mmHg comes out as 1.00000014247 atm and 1 atm comes out as 759.999891726 mmHg. The difference shows up at the eighth digit and never at the third, so 760 mmHg to 1 atm is a fair rounding for anything short of metrology.
- What is 1 atm in mmHg, kPa and psi?
- 759.999891726 mmHg, 101.325 kPa and 14.6959487755 psi, alongside 101,325 Pa and 1.01325 bar. You do not have to ask for those one at a time: put 1 in the From box with atmospheres selected, or use the Swap units button from this page, and the converter works out every pressure unit in the category at once and lists them under the answer.
- Can I convert inches of mercury here?
- Not as a listed unit. The pressure category holds pascals, kilopascals, bar, pounds per square inch, atmospheres and millimetres of mercury, and inHg is not one of them. An inch is exactly 25.4 millimetres, so at the same mercury convention 1 inHg is 25.4 mmHg, which this page shows as 0.033421057393 atm. Multiply your inHg figure by 25.4 and type that. Going the other way, 760 mmHg is 29.9212598425 inHg.
- Why does the list under the answer not repeat mmHg?
- The list shows every other unit in the category, skipping the one you are converting from, so on this page it reads pascals, kilopascals, bar, pounds per square inch and atmospheres. The readout strip also carries an Uncommon units switch labelled Show 1 more, because mmHg is filed as the one uncommon pressure unit. On this page turning it on changes nothing you can see: the unit it would add is the one already sitting in the From box.
- Does it matter whether my figure is gauge or absolute?
- It matters for what the figure describes, and the converter cannot tell the two apart: it changes units and never adds or removes an atmosphere on your behalf. 100 mmHg stated absolutely is 0.131578966114 atm. The same 100 mmHg quoted as a drop below a 760 mmHg ambient describes 660 mmHg absolute, which is 0.868421176352 atm. Settle which convention the number uses before you convert it, because nothing in the arithmetic will flag the mix-up.
- Why does the page open on mmHg and atm when I last converted something else?
- Because a page that names a pair should show that pair. This one sets millimetres of mercury and atmospheres on arrival, ahead of whatever the converter last remembered, and it leaves the main unit converter's own pair alone: go back there and it is still on the units you left it on. The number you last typed does travel with you, along with the uncommon units switch, since that is usually the figure you are still working on.
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.