Every input is converted to pascal, the SI unit, and then out to each target unit. All factors below are exact by definition except where noted.

Absolute or gauge

A pressure unit says nothing about the reference. Gauge pressure is measured against ambient, absolute against vacuum, and the two differ by one atmosphere. The conversion factors are identical either way, so this tool converts whatever you enter, but the reference travels with the number and has to be carried by hand. It is why the same reading appears as psig or psia, and as barg or bara. Confusing them is a common error where it matters most, near atmospheric pressure and in leak testing.

Torr and mmHg

Torr is defined as exactly 1/760 of a standard atmosphere. The conventional millimetre of mercury is defined from a mercury density of 13 595.1 kg/m³ and standard gravity, which makes it 133.322387 Pa. The two differ by 1.4 parts in ten million, far below the accuracy of any gauge reading them, so they are treated as interchangeable here and shown on one tile.

Liquid column units

Inches of mercury and millimetres of water column are defined at a stated liquid density and standard gravity. A real manometer reading depends on the actual temperature of the liquid and the local value of gravity, so a field reading in these units carries an error of a few tenths of a percent against the conventional definition. For anything better than that, use a unit defined in force per area.