The torr (symbol: Torr) or millimeter of mercury (mmHg) is a non-SI unit of pressure. It is the atmospheric pressure that supports a column of mercury 1 millimeter high. The unit is named after Evangelista Torricelli, Italian physicist and mathematician, for his discovery of the principle of the barometer in 1643. Look up si, Si, SI in Wiktionary, the free dictionary. ... The use of water pressure - the Captain Cook Memorial Jet in Lake Burley Griffin in Canberra, Australia. ... Diurnal (daily) rhythm of air pressure in northern Germany (black curve is air pressure) Atmospheric pressure is the pressure at any point in the Earths atmosphere. ... General Name, Symbol, Number mercury, Hg, 80 Chemical series transition metals Group, Period, Block 12, 6, d Appearance silvery Standard atomic weight 200. ... A millimetre (American spelling: millimeter), symbol mm is an SI unit of length that is equal to one thousandth of a metre. ... Evangelista Torricelli portrayed on the frontpage of Lezioni dEvangelista Torricelli. ... A barometer is an instrument used to measure atmospheric pressure. ... // Events January 21 - Abel Tasman discovers Tonga February 6 - Abel Tasman discovers the Fiji islands. ...

One way to define pressure is in terms of the height of a column of fluid that may be supported by that pressure; or the height of a column of fluid that exerts that pressure at its base. Although a manometer may use any fluid in principle, common fluids like water give heights that cannot be contained in a normal room. A water column needs to be of the order of 10 metres high to exert 1 atmosphere of pressure. Therefore a very dense fluid is required — mercury. Normal atmospheric pressure can support around 760 mm (29.92 in) of mercury; hence 1/760 of an atmosphere, or 1 mm of mercury (mmHg), has been a convenient measure of pressure for a long time, and is sometimes also called a torr.

Because the standard atmosphere has been precisely defined (10th CGPM, 1954), and the standard atmosphere had previously been defined as 760 mmHg exactly, those two definitions are now combined to define the torr as exactly 101325/760 ≈ 133.3223684 pascals. Although the pascal is now the more commonly used unit of pressure, the torr is still used in high vacuum engineering, particularly where pressures are low enough that viscosity is absent. Standard atmosphere (symbol: atm) is a unit of pressure. ... The Conférence générale des poids et mesures (General Conference on Weights and Measures or CGPM) is one of the three organizations established to maintain the SI system under the terms of the Metre Convention (1875). ... Year 1954 (MCMLIV) was a common year (link will display full calendar) of the Gregorian calendar. ... The pascal (symbol: Pa) is the SI derived unit of pressure or stress (also: Youngs modulus and tensile strength). ... -1... Viscosity is a measure of the resistance of a fluid to deform under shear stress. ...

The torr, usually under the millimeter of mercury name, remains a common unit for the measurement of gas and blood pressure in much of the world. This article does not cite any references or sources. ... A sphygmomanometer, a device used for measuring blood pressure. ...

mmHg is also used in the United Kingdom as a measure of Intraocular pressure (IOP) within the eye, especially in patients who suffer from glaucoma. Anything between 12 mmHg and 22 mmHg is considered normal. Intraocular pressure is the fluid pressure inside the eye. ...

Although they are synonyms in practice, the torr and millimeter of mercury are very slightly different by virtue of their definitions in British Standard BS 2520 ([1], [2]). While the torr is defined as given above, the millimeter of mercury (called the "conventional millimeter of mercury") is defined by the World Meteorological Organization [3] as "the pressure exerted at the bottom of a vertical column exactly 1 mm deep of a fluid whose density is exactly 13.5951 g/cm³, at a location where the acceleration due to gravity is exactly 980.665 cm/s²" [4]. The "conventional density of mercury" used makes 760 mmHg equal a pressure of exactly 101325.0144354 Pa, a percentage difference from the standard atmosphere of about 0.14 μPa/Pa (i.e., 0.000014 %). Such a small difference is utterly negligible in most practical applications. The World Meteorological Organization (WMO) is an intergovernmental organization with a membership of 187 Member States and Territories. ... Standard atmosphere (symbol: atm) is a unit of pressure. ...

'The Torr' is also the name given to a Bristol based rock band which formed in 1998 and are still performing and recording today. Noteable members include: Jon Steadman, Neil Berry & James Trotham.

Example reading: 1 Pa = 1 N/m²  = 10⁻⁵ bar  = 10.197×10⁻⁶ at  = 9.8692×10⁻⁶ atm ....etc.
Note: mmHg is an abbreviation for millimetres of mercury. The pascal (symbol: Pa) is the SI derived unit of pressure or stress (also: Youngs modulus and tensile strength). ... The bar (symbol bar), decibar (symbol dbar) and the millibar (symbol mbar, also mb) are units of pressure. ... A technical atmosphere (symbol: at) is a non-SI unit of pressure equal to 1 kilogram-force per square centimeter, i. ... Standard atmosphere (symbol: atm) is a unit of pressure. ... A pressure gauge reading in PSI (red scale) and kPa (black scale) The pound-force per square inch (symbol: lbf/in²) is a non-SI unit of pressure based on avoirdupois units. ... The newton (symbol: N) is the SI unit of force. ... In physics, the dyne is a unit of force specified in the centimetre-gram-second (cgs) system of units, symbol dyn. One dyne is equal to exactly 10-5 newtons. ... The deprecated unit kilogram-force (kgf) or kilopond (kp) is the force exerted by one kilogram of mass in standard Earth gravity (defined as exactly 9. ... Standard atmosphere (symbol: atm) is a unit of pressure. ... The pound-force is a non-SI unit of force or weight (properly abbreviated lbf or lbf). The pound-force is equal to a mass of one pound multiplied by the standard acceleration due to gravity on Earth (which is defined as exactly 9. ...

See also

• inHg (Inches of mercury)
• cmH₂O

Inches of mercury or inHg is a non SI unit for pressure. ... A centimeter (centimetre) of water or cmH2O is a somewhat outdated unit for pressure. ...

External links

• NPL - pressure units