Torr to Atm Converter
Convert torr to atmospheres and atm to torr, including vacuum pressures in scientific notation, with pascals, millibar and psi alongside.
1 atm = 760 Torr = 101,325 Pa
Tip: type very small pressures in E notation, for example 5e-7 for 5 × 10⁻⁷ Torr.
760 Torr = 1 atm
The torr is defined as exactly 1/760 of a standard atmosphere, so converting is a single division or multiplication. Divide torr by 760 to get atmospheres (95 Torr = 0.125 atm), and multiply atmospheres by 760 to get torr. In SI units, 1 Torr is about 133.322 Pa.
Reference Pressures in Torr and atm
Altitude figures are typical: actual air pressure changes with the weather.
| Pressure | Torr | atm | Pa |
|---|---|---|---|
| Standard atmosphere, sea level | 760 | 1 | 101,325 |
| Denver, about 1,600 m (typical) | 630 | 0.828947 | 83,993.092105 |
| Summit of Everest (typical) | 253 | 0.332895 | 33,730.559211 |
| Water vapour pressure at 25 °C | 23.76 | 0.031263 | 3,167.739474 |
| Rotary vane pump base pressure | 0.001 | 1.316 × 10⁻⁶ | 0.133322 |
| Ultra-high vacuum chamber | 1 × 10⁻¹⁰ | 1.316 × 10⁻¹³ | 1.333 × 10⁻⁸ |
Vacuum Ranges in Torr
Torr is still the everyday unit in vacuum work, especially in the US. Vacuum quality is usually described in ranges, each spanning several powers of ten. That's why vacuum pressures are almost always written in scientific notation.
| Range | Torr | Typical use |
|---|---|---|
| Low (rough) vacuum | 760 to 1 | Vacuum packing, filtration, degassing |
| Medium vacuum | 1 to 10⁻³ | Freeze drying, distillation, light bulbs |
| High vacuum | 10⁻³ to 10⁻⁹ | Thin-film coating, electron microscopes |
| Ultra-high vacuum | below 10⁻⁹ | Surface science, particle accelerators |
Worked Example: A Vacuum Pump's Base Pressure
A rotary vane pump's spec sheet lists an ultimate pressure of 1 × 10⁻³ Torr. A European supplier quotes its pump in millibar. How do they compare?
Step 1: Torr to atmospheres
Step 2: Torr to pascals and millibar
The pump reaches about 1.3 × 10⁻³ mbar. Torr and millibar are close in size (1 Torr ≈ 1.333 mbar), so a pump rated at 1 × 10⁻³ mbar is slightly better than this one.
Using Torr in the Ideal Gas Law
In PV = nRT, the pressure unit has to match the gas constant. With R = 0.082057 L·atm/(mol·K), convert torr to atm first: a 95 Torr reading becomes 0.125 atm. Alternatively, use R = 62.364 L·Torr/(mol·K) and keep the torr value as it is. Mixing the two makes the pressure 760 times too large.
Gas-law calculations need absolute pressure. Many vacuum gauges read absolute pressure. Ordinary dial gauges read relative to the surrounding air, and the converter doesn't make that adjustment for you.
Torr vs mmHg
The torr was named after Evangelista Torricelli and originally meant one millimetre of mercury. The two units are now defined separately: 1 Torr is exactly 1/760 atm (133.32237 Pa), while 1 mmHg is 133.322387 Pa. They differ by about 0.000014%, so they're interchangeable for anything outside metrology. Medicine still uses mmHg, for blood pressure for example, while vacuum and laboratory work uses Torr.
Frequently asked questions
How many torr are in 1 atm?
Exactly 760. That's the definition of the torr.
Why does a small torr value show in scientific notation?
Vacuum pressures span many powers of ten. 1 × 10⁻⁶ Torr is 1.3 × 10⁻⁹ atm, which would round to 0 as a plain decimal. Scientific notation keeps the real value visible.
Is 1 Torr the same as 1 millibar?
No. 1 Torr ≈ 1.333 mbar, so 1 mbar ≈ 0.75 Torr. They're close enough that spec sheets in both units look similar, so always check which one is quoted.
Can pressure in torr be negative?
No. Absolute pressure can't go below a perfect vacuum (0 Torr), so the converter rejects negative values. A "negative" reading on a dial gauge is relative to the surrounding air.
Sources
- NIST Special Publication 811: definitions of the torr, standard atmosphere and mmHg.
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