What Is Torr (torr)?
Torr is a unit used to measure pressure. Pressure tells us how strongly a gas or liquid pushes on a surface. One torr is a small amount of pressure, useful when we talk about vacuums, blood pressure, and scientific experiments.
The torr is not part of the modern SI system, which uses the pascal, but it is still very common in labs, physics, and some medical areas because it is simple and closely linked to the atmosphere around us.
Definition
In modern terms, the torr has an exact definition:
- 1 torr equals exactly 101325 divided by 760 pascals.
- This is about 133.322 pascals (Pa).
The atmosphere around Earth at sea level has a pressure of about 1 standard atmosphere. The torr is defined so that:
- 1 atmosphere (atm) equals exactly 760 torr.
- So 1 torr equals 1 760 of an atmosphere.
This makes the torr very handy when dealing with fractions of normal air pressure, such as in vacuum systems or gas experiments.
History / Origin
The torr is named after Evangelista Torricelli, an Italian physicist and mathematician from the 1600s. He was a student of Galileo and is famous for inventing the mercury barometer, one of the first reliable tools to measure air pressure.
In Torricelli’s classic experiment, he filled a glass tube with mercury, turned it upside down, and placed it in a dish of mercury. Part of the mercury stayed in the tube, supported by the pressure of the air on the dish. The height of the mercury column showed the air pressure.
For a long time, people measured pressure by the height of this mercury column, in millimeters of mercury, written as mmHg. One common reference level was 760 mmHg for standard atmospheric pressure at sea level.
Later, the name torr was created to honor Torricelli and to replace the older mmHg term with a more precise and standard definition. The torr was carefully defined using the atmosphere and pascal so it could fit better with modern SI units.
Symbol & Abbreviation
The torr uses simple symbols and abbreviations:
- Name torr
- Symbol torr (all lowercase)
Some important notes:
- The word Torr comes from a name, but the symbol is usually written in lowercase as torr.
- The older unit mmHg (millimeter of mercury) is close in size to the torr, but they are not defined in exactly the same way.
- In formal science and engineering writing, you should use torr for this unit and Pa for pascals.
Current Use Around the World
While the official SI unit of pressure is the pascal, the torr is still widely used because it is practical and familiar in certain fields.
Common areas where torr is used
- Vacuum technology scientists and engineers use torr to describe very low pressures in vacuum chambers, pumps, and space simulation equipment.
- Physics and chemistry experiments that deal with gases, plasmas, and thin films often use torr to state pressure.
- Surface science and materials research where clean, low pressure environments are needed.
Medical connection
- Blood pressure is usually measured in mmHg, which is almost the same size as the torr.
- Because 1 mmHg is very close to 1 torr, many people in medicine and physiology think in these units when talking about pressures in the body.
Official status
- The torr is not an SI unit, so scientific standards prefer the pascal.
- However, many technical communities still use torr daily, so it remains an important practical unit in real life.
Example Conversions
Here are some useful conversion factors. You can use them to move between torr and other common pressure units.
Basic exact relationships
- 1 torr = 101325 760 Pa ≈ 133.322 Pa
- 1 atm = 760 torr
Torr to pascal (Pa)
- To convert from torr to Pa, multiply by 133.322.
- To convert from Pa to torr, divide by 133.322.
Worked examples
- 50 torr to Pa
50 × 133.322 ≈ 6666 Pa - 760 torr to Pa
760 × 133.322 ≈ 101325 Pa, which is about 1 atm - 10 torr to Pa
10 × 133.322 ≈ 1333 Pa
Torr to atmosphere (atm)
- To convert from torr to atm, divide by 760.
- To convert from atm to torr, multiply by 760.
Examples
- 380 torr to atm
380 ÷ 760 = 0.5 atm - 1 atm to torr
1 × 760 = 760 torr
Torr to bar
- 1 bar ≈ 750.062 torr
- 1 torr ≈ 0.001333 bar
Example
- 500 torr to bar
500 × 0.001333 ≈ 0.666 bar
Torr to millimeters of mercury (mmHg)
The torr was designed to be very close to 1 mmHg, but because of modern exact definitions, there is a tiny difference.
- 1 torr ≈ 0.999999 mmHg (almost exactly 1 mmHg)
- 1 mmHg ≈ 1.000001 torr
In everyday use, people often treat 1 torr and 1 mmHg as the same, but precision work may keep the small difference.
Torr to psi (pounds per square inch)
- 1 psi ≈ 51.715 torr
- 1 torr ≈ 0.019336 psi
Example
- 1000 torr to psi
1000 × 0.019336 ≈ 19.34 psi
Related Units
The torr is one of several ways to measure pressure. Here are the most closely related units.
- Pascal (Pa) the SI unit of pressure. 1 Pa is 1 newton of force per square meter. 1 torr ≈ 133.322 Pa.
- Atmosphere (atm) based on average air pressure at sea level. 1 atm = 760 torr.
- Bar a convenient unit in engineering. 1 bar ≈ 100000 Pa ≈ 750.062 torr.
- Millimeter of mercury (mmHg) an older unit based on the height of a mercury column in a barometer. Almost equal to 1 torr, but defined slightly differently.
- Pounds per square inch (psi) common in the United States for tires, hydraulics, and gas systems. 1 psi ≈ 51.715 torr.
All these units describe the same physical idea, pressure, but they are used in different fields, countries, or types of work.
FAQs
What is a torr in simple words
A torr is a small unit that tells you how strongly gas or liquid pushes on a surface. It is about one seven hundred sixtieth of normal air pressure at sea level.
Why is it called torr
It is named after Evangelista Torricelli, the scientist who invented the mercury barometer and helped discover how to measure air pressure.
Is torr an SI unit
No. The official SI unit of pressure is the pascal, Pa. The torr is a non SI unit, but is still widely used in some scientific and technical fields.
How many pascals are in 1 torr
Exactly 101325 760 pascals, which is about 133.322 pascals.
How is torr related to atmosphere
By definition, 1 atmosphere equals 760 torr. So 1 torr equals 1 760 of an atmosphere.
Are torr and mmHg the same
They are almost the same size. Historically they were treated as equal, but in strict modern definitions there is a very small difference. For most everyday uses, they can be treated as equal.
Where is torr still used today
Torr is common in vacuum science, physics labs, surface science, and some engineering work where low pressures are important. It also shows up when comparing with blood pressure readings in mmHg.
Why do scientists sometimes prefer torr instead of pascal
For very low pressures, like in vacuum systems, torr values are often easier to read and remember. Saying 0.001 torr feels simpler than saying about 0.133 Pa, even though they describe the same pressure.
Can I convert torr to psi for practical uses
Yes. Use 1 torr ≈ 0.019336 psi. Multiply torr by 0.019336 to get psi, or divide psi by 0.019336 to get torr.
Should I use torr or pascal in school work
If your teacher or textbook does not say otherwise, use pascal, since it is the official SI unit. It is fine to learn about torr as a helpful extra unit, especially for vacuum and gas pressure topics.