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Millimetre of mercury
Manometric unit of pressure / From Wikipedia, the free encyclopedia
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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]
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 |
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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.