This converter turns a vacuum gauge reading into other units. Enter the value and its unit, pick whether the gauge reads absolute or gauge pressure, and the page lays out the absolute pressure and the vacuum below atmosphere in nine units side by side, US units first: psi, inches of mercury, then Torr, microns, Pa, kPa, hPa, bar and atm. A dial reading in inches of mercury vacuum can be entered directly with the inHg vacuum option.
Every conversion rests on the definition of standard atmosphere, namely 1 atm equals 101,325 Pa, 760 Torr, 760 mmHg and 1.01325 bar. The Torr factor is derived from that definition by dividing 101,325 by 760, and the US units use 1 psi = 6,894.757 Pa and 1 inHg = 3,386.389 Pa (mercury at 32 °F). The reference atmosphere defaults to 14.696 psi, can be edited or switched to inHg or kPa, and the value applied is printed with the result. For example 5 inHg absolute is about 24.92 inHg vacuum, or 2.456 psia. Figures current as of October 2026.
Use psia for absolute and psig for gauge readings by choosing the reading basis. A negative number on the absolute basis stops the calculation with a note to switch to the gauge basis instead. Pump sizing, pump down time and corrections for the gas species are not covered. This calculator is for reference and does not replace design. Review by a qualified engineer is required.
Frequently Asked Questions
Absolute pressure counts up from perfect vacuum, while vacuum counts how far the reading sits below atmosphere. An absolute 760 Torr is zero vacuum, and an absolute 1 Torr is a vacuum of 759 Torr.
Vacuum is measured against the atmospheric pressure of the day, which differs from the standard value at altitude or in a low pressure system. The default is the standard atmosphere of 14.696 psi (29.921 inHg, 101.325 kPa) and you can enter the local reading instead.
Plain inHg here is an absolute pressure, counted from perfect vacuum. Inches of mercury vacuum is what a compound or vacuum gauge shows, counted down from atmosphere, so 0 inHg vacuum is atmosphere and about 29.92 inHg vacuum is close to perfect vacuum at sea level.