inHg

inch of mercury

Pressureexact by definition

The inch of mercury is exactly 25.4 millimetres of mercury, which is 3386.388640341 pascals under the conventional mercury density of 13 595.1 kg/m³ and standard gravity. The value is exact given that convention. Standard atmospheric pressure is 29.92 inHg, the number on every North American altimeter setting.

Watch out: Engine vacuum and vacuum-system readings in inHg are usually measured downward from atmosphere, so "20 inches of vacuum" means about 9.9 inHg absolute, not 20. Aviation and weather use inHg absolute. Read which convention the instrument uses before converting.

1 inHg 3.3863886 kPa