What is torr?
A torr is a pressure unit equal to approximately 1/760 of an atmosphere. It is used in vacuum technology, low-pressure experimental physics, and blood pressure measurement in older clinical literature.
Real-world uses
Torr is used in vacuum technology, semiconductor manufacturing, and blood pressure measurement (mmHg ≈ torr). Vacuum chambers for electron beam welding operate at about 10⁻⁵ torr, and freeze-drying processes typically operate at 0.1–1 torr.
History
Named after Evangelista Torricelli, who invented the mercury barometer in 1644. The torr was defined to approximate the pressure exerted by 1 mm of mercury. It was formally standardized as 1/760 of a standard atmosphere.
Common mistakes
Assuming torr and mmHg are exactly the same—they are nearly identical but differ by about 0.000015%. For most purposes they are interchangeable, but ultra-precise vacuum work may require distinction.
What is pound per square inch?
Pound per square inch (psi) is an imperial pressure unit widely used in the United States for tire inflation, hydraulic system pressures, gas cylinder ratings, and plumbing specifications.
Real-world uses
PSI is the standard pressure unit in the United States for tyre inflation (typically 30–35 psi for cars), compressed air tools, hydraulic systems, and water pressure. HVAC systems, fire extinguisher ratings, and pressure cooker specifications use psi in North America.
History
Pounds per square inch emerged naturally from the Imperial/US customary system, combining the pound-force with the square inch. It became the dominant pressure unit in American industry and remains deeply embedded in US engineering standards and building codes.
Common mistakes
Not distinguishing between psi (absolute, psia) and psig (gauge, relative to atmosphere). A tyre reading of 32 psig actually means about 46.7 psia. Also, confusing psi with kPa when using equipment from metric countries.
When is this conversion used?
Tyre pressure gauges, HVAC systems, and industrial equipment may use different pressure units depending on the manufacturer and region. Converting between psi, bar, and kPa is common in automotive and engineering work.
Worked examples
1 torr = 0.01933677 pound per square inch
1 pound per square inch = 6,894.75729317 pascal
How to convert torr to pound per square inch
To convert torr to pound per square inch, multiply the value by 0.01933677.
To convert pound per square inch back to torr, multiply by 51.71493257.
Measurement standards
The pascal (Pa) is the SI derived unit of pressure, defined as one newton per square metre. The World Meteorological Organization mandates the hectopascal (hPa) for atmospheric pressure reporting in aviation and weather services.
Did you know?
The pressure at the bottom of the Mariana Trench, nearly 11 km deep, exceeds 1,086 bar — over a thousand times atmospheric pressure. At this depth, water is compressed by about 5%, making it measurably denser than at the surface.
Quick reference: torr to pound per square inch
| torr | pound per square inch |
|---|---|
| 0.1 | 0.00193368 |
| 0.5 | 0.00966839 |
| 1 | 0.01933677 |
| 2 | 0.03867355 |
| 5 | 0.09668387 |
| 10 | 0.19336775 |
| 25 | 0.48341937 |
| 50 | 0.96683874 |
| 100 | 1.93367747 |
| 250 | 4.83419368 |
| 500 | 9.66838735 |
| 1,000 | 19.3367747 |
Common values
| torr | pound per square inch | |
|---|---|---|
| Car tyre | 1,650.13570195 torr | 31.9083023 pound per square inch |
| Standard atmosphere | 760 torr | 14.69594878 pound per square inch |
| Blood pressure (systolic) | 120.00986923 torr | 2.3206038 pound per square inch |
| Deep-sea submersible | 825,067.85097429 torr | 15,954.15115032 pound per square inch |
| Bicycle tyre | 4,650.38243276 torr | 89.92339739 pound per square inch |