Inches of mercury, (inHg and "Hg It is defined as the pressure exerted by a circular column of mercury of 1 inch in height at 32 °F (0 °C) at the standard acceleration of gravity. 1 inHg = 3386.389 Pa at 0 °C. In older literature, an "inch of mercury" is based on the height of a column of mercury at 60 °F (15.6 °C) 1 inHg60 °F = 3376.85 Pa In English units: 1 inHg = 0.491 098 psi, or 2.036 254 inHg = 1 psi.