torr

Convert between torrs and other major units of pressure

A unit of atmospheric pressure, = exactly ¹⁄₇₆₀ atmosphere = exactly ¹⁰¹³²⁵⁄₇₆₀ pascals or approximately 133.322 368 pascals. Symbol, Torr.

It is named for the Italian physicist Evangelista Torricelli (1608 – 1647).

To within 1 part per million, 1 torr is equal to the pressure of a column of mercury 1 millimeter high at Earth's surface. See conventional millimeter of mercury.

According to the current national standard in the United States¹, the torr is not to be used. The pascal should be used instead.

In 1971, the European Economic Community directed that use of this unit cease by 31 December 1977

1. IEEE/ASTM SI 10™-2002.
American National Standard for Use of the International System of Units (SI): The Modern Metric System.
New York: IEEE, 30 December 2002.

See Section 3.3.3.

2. European Economic Community, Council Directive of 18 October 1971 on the approximation of the laws of the Member States relating to units of measurement (Directive 71/354/EEC), Annex, Chapter III.

sources

Prof. Gopal noted that the decline in use of the torr and mbar in favour of the SI unit pascal has taken about sixty years.

Bureau International des Poids et Mesures.
Comité International des Poids et Mesures.
Procès-verbaux de la 87e session.
Report of the 87th Meeting, 1998.
Tome 66.
Sèvres: BIPM, 1999.
Page 182.

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