# Inch of mercury

**Inch of mercury** (**inHg** and **″Hg**) is a non-SI unit of measurement for pressure. It is used for barometric pressure in weather reports, refrigeration and aviation in the United States.

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Inch of mercury | |
---|---|

General information | |

Unit of | Pressure |

Symbol | inHg or ″Hg |

Conversions | |

1 inHg in ... | ... is equal to ... |

SI units | 3.38639 kPa |

United States customary units | 0.491154 psi |

It is the pressure exerted by a column of mercury 1 inch (25.4 mm) in height at the standard acceleration of gravity. Conversion to metric units depends on the temperature of mercury, and hence its density; typical conversion factors are:[1]

Conditions | Pressure |
---|---|

conventional | 3386.389 pascals |

32 °F (0 °C) | 3386.38 pascals |

60 °F (16 °C) | 3376.85 pascals |

In older literature, an "inch of mercury" is based on the height of a column of mercury at 60 °F (15.6 °C).[1]

- 1 inHg
_{60 °F}= 3,376.85 pascals (33.7685 hPa)

In Imperial units: 1 inHg_{60 °F} = 0.489 771 psi, or 2.041 771 inHg_{60 °F} = 1 psi.