Pressure is defined as force per unit area. Pressure above atmospheric is mostly measured in pounds per square inch (PSI), or in kilo gram per square centimeter (kg/cm2) gauge or absolute. For lower pressure (below about 10 psi), inches or cms. of water or mercury column are frequently used. For near atmospheric pressure, we refer more commonly to millimeters of mercury column (or torr).
The SI unit of pressure is Newton per square meter, or PASCAL (Pa). One atmospheric pressure (atm) is equal to 101325 Pa or 101.325 Kpa. More recently, bar is also being used for higher ranges. A bar is 0.987 atm, or approximately 14.5 PSI. A conversion table for more commonly used pressure units is given here.
Pressure Conversion Table:
From atmospheric Psi Bar mmHg (torr):
Atmospheric 1.000 14.696 1.0133 760.00
Psi 0.068 1.000 0.0689 51.50
Bar 0.987 14.504 1.000 750.06
Kg/sq.cm 0.9678 14.223 0.9807 735.56
MmHg(torr) 0.0013 0.019 0.013 1.00
Mm(WC) 0.0001 0.0014 0.0001 0.0736HgHJH