Pressure Equations

Pressure Conversion Factors

psi = in of H₂0 x 0.0361*
psi = ft of H₂0 x 0.4335*
psi = mm of H₂0 x 0.0014*
psi = cm of H₂0 x 0.0142*
psi = in of Hg x 0.4912
psi = mm of Hg x 0.0193
psi = cm of Hg x 0.193
psi = kg/cm² x 14.22*
psi = bar x 14.50
psi = mbar x 0.0145
psi = Pascals x 1.45 x 10⁴*
psi = Kilopascals x 0.1450
psi = atm x 14.696
in of H₂0 = psi x 27.71*
ft of H₂0 = psi x 2.31*
mm of H₂0 = psi x 703.1*
cm of H₂0 = psi x 70.31*
in of Hg = psi x 2.036
mm of Hg = psi x 57.71
cm of Hg = psi x 5.771
kg/cm² = psi x 0.0703*
bar = psi x 0.0689
mbar = psi x 68.95
Pascals = psi x 6895
Kilopascals = psi x 6.895
atm = psi x 0.068

Air Pressure / Flow Formulas

Pv* = ( V /4004)²*

Pv = Pt - Ps

Where: V = Velocity (feet per minute)
Pv = Velocity Pressure (inches water column)
Pt = Total Pressure (inches water column)
Ps = Static Pressure (inches water column)
*Pv may be determined by a Pitot Tube.

Head Pressure Formulas

Head (feet) = psi x 2.31 / Specific Gravity
psi = Feet Head x Specific Gravity / 2.31

Pressure Definitions

Absolute Pressure

The sum of gauge pressure and atmospheric pressure.

Atmospheric Pressure

The pressure existing at the surface of the earth caused by the weight of a column of air above the point of measurement. Atmospheric Pressure varies with altitude and weather conditions, but 14.696 psia is generally accepted except in high altitude locations.

Gauge Pressure

A pressure reading above Atmospheric Pressure. Most instruments read gauge pressure.

Pitot Tube

A tube that is inserted in a duct to measure both total pressure and static pressure, and has separate connections so that each pressure may be sensed.

Pressure Transducer

A device that converts a pressure input into an electrical signal.

Snubber

A device used to dampen pulsations to pressure instruments.

Static Pressure

The outward push of a fluid against the walls of a container.

Total Pressure

The sum of Static Pressure and Velocity Pressure.

Velocity Pressure

The pressure exerted by the velocity of a fluid. Velocity pressure is generally obtained by measuring Total Pressure and Static Pressure and subtracting the Static Pressure from Total Pressure. The remainder is Velocity Pressure.

* This equation contains subscripts or superscripts which may not be supported by all web browsers. Contact your Kele Sales Representative if there are any questions about this formula.