Torr to atm Conversion Calculator
Enter a pressure in torr and instantly see the equivalent in standard atmospheres (atm), pascals, kilopascals, bar, psi, and inches of mercury. Switch the direction to convert from atm back to torr. The calculator uses the exact defined ratio: 1 atm = 760 Torr.
Formula
Worked example
800 Torr converted to atm: 800 ÷ 760 = 1.052632 atm. In pascals: 1.052632 × 101325 = 106657 Pa. In psi: 106657 ÷ 6894.757 = 15.470 psi.
What is a Torr and where does it come from?
The torr is a unit of pressure named after Evangelista Torricelli, the Italian physicist who invented the mercury barometer in 1644. One torr is defined as exactly 1/760 of a standard atmosphere, which makes it numerically equal to one millimetre of mercury (mmHg) for practical purposes (they differ by less than 0.000015%). At standard sea-level conditions, a column of mercury 760 mm tall exerts exactly 1 atm of pressure, so a 1 mm column exerts 1 Torr. The unit remains widely used in vacuum technology, semiconductor manufacturing, and laboratory science, especially in contexts where pressures well below atmospheric are common.
The conversion formula and why it is exact
The standard atmosphere (atm) is defined as exactly 101,325 pascals, and the torr is defined as exactly 1/760 atm. These are fixed definitions, not measured approximations, so the relationship 1 atm = 760 Torr is mathematically exact. To convert torr to atm, divide by 760. To convert atm to torr, multiply by 760. Rounding only occurs when you choose how many decimal places to display - the ratio itself introduces no error. Converting to other units requires one more step through the pascal: 1 Torr = 101325/760 Pa = 133.322 Pa (to 3 decimal places).
Torr in vacuum science and where these pressures appear in practice
Vacuum technology uses torr far more than atmospheric science does, because the unit is well-suited to the pressure ranges that matter in labs and factories. A rough vacuum pump pulls a system down to about 1 to 10 Torr. A turbomolecular pump reaches 0.001 to 0.0000001 Torr (the high-vacuum range). Ion pumps and bake-out procedures push into the ultra-high-vacuum region below 0.0000001 Torr. Freeze-dryers and vacuum ovens typically operate between 0.01 and 1 Torr. Standard atmospheric pressure is 760 Torr, while weather systems span roughly 680 to 800 Torr at sea level. Knowing how a specific torr value maps to an atm value helps when comparing specifications across instruments calibrated in different units.
Other pressure units and how they relate to Torr
The pascal (Pa) is the SI unit of pressure and the foundation for all other conversions: 1 Torr = 133.322 Pa. The kilopascal (kPa) is 1000 Pa, giving 1 Torr = 0.133322 kPa. The bar is 100,000 Pa, giving 1 Torr = 0.0013332 bar. The millibar (mbar) equals the hectopascal (hPa), both 100 Pa, so 1 Torr = 1.33322 mbar - a useful fact because European and meteorological standards often quote pressures in hPa. One pound per square inch (psi) is 6894.757 Pa, so 1 Torr = 0.019337 psi. For aviation in the United States, pressure altimeters use inches of mercury (inHg): 1 Torr = 1 mmHg = 0.039370 inHg.
Torr to atm quick-reference table
| Torr | atm | kPa | psi | Context |
|---|---|---|---|---|
| 0.001 | 0.0000013 | 0.000133 | 0.0000193 | Ultra-high vacuum (ion pump limit) |
| 0.1 | 0.000132 | 0.01333 | 0.001934 | High vacuum (turbopump range) |
| 1 | 0.001316 | 0.13332 | 0.01934 | Rough vacuum / freeze-dryer |
| 10 | 0.013158 | 1.3332 | 0.19337 | Vacuum drying oven |
| 100 | 0.13158 | 13.332 | 1.9337 | Low vacuum / rough pump limit |
| 250 | 0.32895 | 33.331 | 4.834 | Approx. pressure at 8000 m altitude |
| 530 | 0.69737 | 70.661 | 10.249 | Approx. pressure at 5000 m altitude |
| 760 | 1.00000 | 101.325 | 14.696 | Standard sea-level atmosphere |
| 1000 | 1.31579 | 133.322 | 19.337 | Mild pressurisation |
| 1520 | 2.00000 | 202.650 | 29.392 | 2 atm (e.g. deep-sea or autoclave) |
Common torr values and their equivalents in atm, kPa, and psi.
Frequently asked questions
How many atm is 1 Torr?
1 Torr is exactly 1/760 atm, which equals approximately 0.001316 atm. This is an exact relationship because both units are defined values: the standard atmosphere is defined as exactly 101,325 Pa, and the torr is defined as exactly 1/760 of that.
Is 1 Torr the same as 1 mmHg?
Almost, but not exactly. 1 Torr = 1/760 atm, while 1 mmHg is defined by the density of mercury at 0 degrees Celsius and standard gravity, which gives 1 mmHg = 133.322387 Pa. Since 1 Torr = 133.322368 Pa, the two differ by only about 0.000015%, which is negligible for virtually all practical work. Many sources treat them as identical, and this calculator uses the exact torr definition.
How do I convert atm to Torr?
Multiply the number of atmospheres by 760. For example, 2.5 atm x 760 = 1900 Torr. Use the direction toggle in the calculator above to switch to atm-to-Torr mode and enter your value.
What is 760 Torr in atm?
760 Torr is exactly 1 atm, by definition. This corresponds to standard sea-level atmospheric pressure: 101,325 Pa, 101.325 kPa, 1.01325 bar, or 14.696 psi.
Why is Torr used in vacuum science instead of Pa or bar?
The torr emerged from mercury-manometer measurements that were central to early vacuum research, and the unit stuck because it maps intuitively onto millimetres of mercury - which is what vacuum gauges historically measured. Modern SI usage favors the pascal, but legacy instrument specifications, vacuum pump datasheets, and much published research still quote pressures in torr, particularly in the 0.001 to 100 Torr range that covers most laboratory vacuums.
What is standard atmospheric pressure in Torr?
Exactly 760 Torr. The torr was originally defined to make this relationship come out to a round number: 1 atm = 760 mmHg, and the torr was subsequently defined as 1/760 atm to formalise the definition without depending on a physical mercury column.