Home >> Science & Nature >> Science

How to Convert MM Vacuum to PSIG

Scientists working with systems under vacuum have several units which they can use to describe the very low pressures at which they are conducting experiments. One such unit is the millimeter mercury (mm Hg). Another common means of measuring pressure is pounds per square inch (psi) which can be recorded in either psi gauge (psig) or psi absolute (psia). When converting from mm Hg to psig, you have to remember that gauge pressure is set to read zero at normal atmospheric pressure.

Things You'll Need

Calculator

Instructions

- 1
  Enter your pressure value, in units of mm Hg, into the calculator. For example, if the vacuum pressure reading was 25 mm Hg, enter 25.
- 2
  Multiply the vacuum pressure reading value you just entered by 0.0193. This is the conversion factor between mm Hg and psi. The result will be the pressure in units of psia. In the case of the example, you would calculate 25 x 0.0193 which equals 0.483 psia.
- 3
  Subtract 14.7 psi from your previous result. This subtracts standard atmospheric pressure and changes the reading from units of psia to psig. In the example, you would subtract 14.7 from 0.483 to obtain a value of -14.22 psig.

Science