# Millimetre of mercury

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 or mm Hg |

Conversions | |

1 mmHg in ... | ... is equal to ... |

SI units | 133.322 Pa |

English Engineering units | 0.01933678 lbf/in^{2} |

Although not an SI unit, the millimetre of mercury is still routinely used in medicine, meteorology, aviation, and many other scientific fields.

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.