Millimetre of mercury

millimetre of mercury
millimetre of mercury
Unit of	Pressure
Symbol	mmHg, mm Hg
Conversions
1 mmHg in ...	... is equal to ...
SI units	133.322 Pa
English Engineering units	0.01933678 lbf/in2

A millimetre of mercury is a manometric unit of pressure, formerly defined as the extra pressure generated by a column of mercury one millimetre high, and currently defined as exactly 133.322387415 pascals^[1] or exactly 133.322 pascals.^[2] It is denoted mmHg^[3] or mm Hg.^[4]^[2]

Although not an SI unit, the millimetre of mercury is still often encountered in some fields; for example, it is still widely used in medicine, as demonstrated for example in the medical literature indexed in PubMed.^[5] For example, the U.S. and European guidelines on hypertension, in using millimeters of mercury for blood pressure,^[6] are reflecting the fact (common basic knowledge among health care professionals) that this is the usual unit of blood pressure in clinical medicine.

One millimetre of mercury is approximately 1 torr, which is 1/760 of standard atmospheric pressure (101325/760 ≈ 133.322368 pascals). Although the two units are not equal, the relative difference (less than 0.000015%) is negligible for most practical uses.

^ BS 350: Part 1: 1974 – Conversion factors and tables. British Standards Institution. 1974. p. 49.
^ ^a ^b Council Directive 80/181/EEC of 20 December 1979 on the approximation of the laws of the Member States relating to units of measurement and on the repeal of Directive 71/354/EEC of the European Economic Community
^ International Bureau of Weights and Measures (2006), The International System of Units (SI) (PDF) (8th ed.), p. 127, ISBN 92-822-2213-6, archived (PDF) from the original on 2021-06-04, retrieved 2021-12-16
^ "AMA Manual of Style Online". American Medical Association. Retrieved 2018-02-24.
^ National Center for Biotechnology Information of the National Library of Medicine of the United States. "Articles demonstrating pressures in mm Hg". PubMed. Retrieved 2023-09-02.
^ Gijón-Conde, T; Sánchez-Martínez, M; Graciani, A; Cruz, JJ; López-García, E; Ortolá, R; Rodríguez-Artalejo, F; Banegas, JR (July 2019). "Impact of the European and American guidelines on hypertension prevalence, treatment, and cardiometabolic goals". Journal of Hypertension. 37 (7): 1393–1400. doi:10.1097/HJH.0000000000002065. PMID 31145710. S2CID 86674318.

[1] BS 350: Part 1: 1974 – Conversion factors and tables. British Standards Institution. 1974. p. 49.

[EEC-80-181-2] Council Directive 80/181/EEC of 20 December 1979 on the approximation of the laws of the Member States relating to units of measurement and on the repeal of Directive 71/354/EEC of the European Economic Community

[3] International Bureau of Weights and Measures (2006), The International System of Units (SI) (PDF) (8th ed.), p. 127, ISBN 92-822-2213-6, archived (PDF) from the original on 2021-06-04, retrieved 2021-12-16

[AMA_MOS-4] "AMA Manual of Style Online". American Medical Association. Retrieved 2018-02-24.

[NCBI-NLM-PubMed-mm-Hg-5] National Center for Biotechnology Information of the National Library of Medicine of the United States. "Articles demonstrating pressures in mm Hg". PubMed. Retrieved 2023-09-02.

[pmid_31145710-6] Gijón-Conde, T; Sánchez-Martínez, M; Graciani, A; Cruz, JJ; López-García, E; Ortolá, R; Rodríguez-Artalejo, F; Banegas, JR (July 2019). "Impact of the European and American guidelines on hypertension prevalence, treatment, and cardiometabolic goals". Journal of Hypertension. 37 (7): 1393–1400. doi:10.1097/HJH.0000000000002065. PMID 31145710. S2CID 86674318.

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