The symbol Torr stands for the unit of pressure torr, which is equal to exactly 1/760 atm or 133.322 Pa.
There are many other units of pressure, but torr is useful for measuring small pressures, like in vacuum chambers. Since the atmospheric pressure is 760 torr, vacuuming even to 1% of a standard atmosphere can still be written in torr without scientific notation.
One confusing note about torr: the unit is called “torr” and written with a lowercase t. However, the symbol/abbreviation for torr is “Torr”, with a capital T. So you would say, “The atmospheric pressure in torr is 760 Torr.”
The torr originally developed to be equivalent to 1 mmHg. Old pressure gauges used fluid (like mercury) in a tube; by measuring the liquid’s height change in the tube, you could calculate the pressure difference. This kind of pressure unit is called a “manometric” unit, and mmHg was probably the most-common one. With the measuring ability of the day, it seemed that about 760 mmHg was the pressure of 1 standard atmosphere.
Now, torr is defined in terms of the standard atmosphere, so that it is exactly 760 Torr per 1 atm. However, mmHg kept its original meaning, so now the units are slightly different. 1 mmHg is now 1.00000014247 Torr.
The torr is a non-metric, non-SI unit for pressure.
|1 Torr =||133.3 Pa||1.316*10-3 atm||1 mmHg|
The torr is named after Evangelista Torricelli, who laid the foundation for the barometer (a device that measures air pressure).
This article was a definition of Torr. If you are interested in all the different, strange units that are used to measure pressure, I wrote an entire article explaining what each unit is, and how to convert between them. Or, if there is a unit you are especially interested in, you can check out one of the other unit definitions I’ve written.
Other Pressure Measurements:
mbar or bar
psi or ksi