Pressure Measurement · Glossary

What is Pressure?

Symbol: pPa, bar, psiPressure Measurement

Pressure is force acting per unit area. In fluids it acts equally in all directions at a point.

Pressure Explained

Pressure is the most measured variable in process plants. It is used directly for control and safety, and indirectly to measure flow, level and density.

The SI unit is the pascal (1 N/m²). Plants mostly use bar, kPa, MPa or psi. Always state whether a value is gauge, absolute or differential.

Pressure Formula

p = F ÷ A

p	pressure (Pa)
F	force (N)
A	area (m²)

Example: 10 bar (1,000,000 Pa) on a 100 mm diameter piston (A = 0.007854 m²) gives F = 7854 N.

Pressure: Typical Values

1 bar	100 kPa = 14.504 psi
1 standard atmosphere	101.325 kPa = 1.01325 bar = 14.696 psi
1 psi	6.895 kPa

Calculators for Pressure

CalculatorPressure Force CalculatorFree online calculator with formula and worked example.CalculatorAbsolute Pressure CalculatorFree online calculator with formula and worked example.

Frequently Asked Questions

What is Pressure?

Pressure is force acting per unit area. In fluids it acts equally in all directions at a point.

Is pressure a vector?

No. Pressure at a point has no direction; it acts equally on any surface placed there. The force it creates on a surface acts normal to that surface.

Which pressure unit should I use?

Use the unit your plant standard specifies, and always add g, a or d (gauge, absolute, differential) to avoid confusion.

Learn more on the blog

Gauge pressure transmitter: working principle and applications

A practical guide on instrumentationblog.in with more detail on pressure and how it is applied on real plants.

Read Full Article

More Pressure Measurement Terms

Pressure termVacuumVacuum is any pressure below atmospheric pressure, from slight suction to near perfect vacuum.Pressure termAtmospheric PressureAtmospheric pressure is the pressure of the air around us; it falls with altitude and varies with weather.Pressure termHydrostatic PressureHydrostatic pressure is the pressure created by the weight of a liquid column; it depends only on height…Pressure termPressure HeadPressure head is pressure expressed as the height of a liquid column that would produce it.Pressure termStatic PressureStatic pressure is the pressure of a fluid measured at right angles to the flow, without the effect of…Pressure termUpper Range LimitUpper range limit is the highest value a transmitter sensor can be calibrated to measure.

All pressure measurement terms · Full glossary A to Z