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# Physics > Pressure Units

The following table shows the various units of pressure used in physics.

The bar, decibar and the millibar (mb) are units of pressure. They are not however SI units, but are accepted for use with the SI system.

When reading from barometers etc, note that mmHg is an abbreviation for millimetres of mercury.

The torr (symbol: Torr) is a non-SI unit of pressure defined as 1/760 of an atmosphere.
The pascal (symbol: Pa) is the SI derived unit of pressure or stress.

The bar, decibar and millibar are defined as:

The three dimensions of light are:
• 1 bar = 100 kPa (kiloPascals) = 1,000,000 dynes centimetre2 (baryes)
• 1 dbar = 0.1 bar = 10 kPa = 100,000 dyn/cm2
• 1 mbar = 0.001 bar = 0.1 kPa = 1 hPa = 1,000 dyn/cm2
(A Pascal is one Newton per square metre)

Pascal
(Pa)
Bar
(bar)
Technical atmosphere
(at)
Atmosphere
(atm)
Torr
(Torr)
Pound-force per
square inch
(psi)
1 Pa ≡ 1 N/m2 10 -5 1.0197×10-5 9.8692×10-6 7.5006×10-3 145.04×10-6
1 bar 100,000 ≡ 106 dyn/cm2 1.0197 0.98692 750.06 14.504
1 at 98,066.5 0.980665 ≡ 1 kgf/cm2 0.96784 735.56 14.223
1 atm 101,325 1.01325 1.0332 ≡ 1 atm 760 14.696
1 torr 133.322 1.3332×10-3 1.3595×10-3 1.3158×10-3 ≡ 1 Torr; ≈ 1 mmHg 19.337×10 -3
1 psi 6,894.76 68.948×10-3 70.307×10-3 68.046×10-3 51.715 ≡ 1 lbf/in2