UNITS OFTEN USED FOR PRESSURE
 

  psi (1) in.H2O (2) in.Hg (3) kPa millibar cm H2O (4) mm Hg (5)
psi 1.000 27.680 2.036 6.8947 68.947 70.308 51.715
in.H2O 3.6127 10-2 1.000 7.3554 10-2 0.2491 2.491 2.5400 1.8683
in.Hg 0.4912 13.596 1.000 3.3864 33.864 34.532 25.400
kPa 0.14504 4.0147 0.2953 1.000 10.000 10.1973 7.5006
millibar 0.01450 0.40147 0.02953 0.100 1.000 1.01973 0.7355
cm H2O 1.4223 10-2 0.3937 2.8958 10-2 0.09806 0.9806 1.000 0.7355
mm Hg (torr) 1.9337 10-2 0.53525 3.9370 10-2 0.13332 1.3332 1.3595 1.000

 
(1) pounds per square inch
(2) at 39 F
(3) at 32 F
(4) at 4 C
(5) at 0 C

Also:
High pressures are often expressed in units of atmospheres (1 atm =1.01325 105 Pa), bar ( 1 bar= 105 Pa), megapascal ( 1Mpa=106), or even megabar ( 1 Mbar = 106). Low pressures of a high vacuum are commonly evaluated in units of torr ( 1 torr = 1 mmHg) or micrometers of mercury (m Hg).


RELATION OF VARIOUS UNITS OF PRESSURE TO THE PASCAL -- (H2O at 60 F, Hg at O C)
 

1 microbar = 0.1 Pa 1 in.H2O = 248.8 Pa
1 m Hg =0.1333 Pa 1 kPa = 1000 Pa
1 N/m2 = 1 Pa 1 ft H2O = 2986 Pa
1 mm H2O = 9.795 Pa 1 in. Hg = 3386 Pa
1 mbar = 100 Pa 1 psi = 6895 Pa
1 mmHg = 133.3 Pa 1 bar = 105 Pa
1 torr = 133.3 Pa 1 atm = 101325 Pa

 
Derived Units: Bold Units have Assigned Symbols, Plain Units do not have Assigned Special Symbols