Pressure calculators

Pressure unit conversion, hydrostatic head and DP level calculations.

Pressure Unit Converter — psig, barg, kPa, kg/cm², mmWC

bar, psi, kPa, kg/cm², mmH2O, inH2O, mmHg, Torr, atm — all at once.

Hydrostatic Pressure / Liquid Head Calculator

Pressure from liquid height and density (and back).

Gauge to Absolute Pressure Converter — barg ↔ bara, psig ↔ psia

psig to psia, barg to bara — with altitude-corrected atmospheric pressure.

About pressure calculations

Pressure is the most measured variable in process plants, and also the most unit-fragmented — the same physical quantity travels under bar, psi, kPa, mmHg, inches of water column, kg/cm² and more, often within a single project. A large share of pressure "errors" are really unit or reference-basis confusions rather than instrument faults.

The reference basis matters as much as the unit. Gauge pressure measures relative to local atmosphere; absolute measures relative to vacuum. Mix them and you introduce roughly 101 kPa of error — which is why almost every gas law calculation, steam table lookup and vacuum measurement starts by settling this question explicitly.

Hydrostatic head is where pressure measurement becomes level measurement: a column of liquid presses down in proportion to its height and density, so a pressure transmitter at the bottom of a tank is really a height gauge with a density assumption built in.

How these tools fit together

  1. Settle the units. Convert everything into one system before calculating. Mixed units in a single calculation are the most common source of pressure errors.
  2. Settle gauge versus absolute. Any calculation involving gas behaviour, steam properties or vacuum needs absolute pressure. Add local atmospheric pressure, corrected for altitude if significant.
  3. Work out the head. For level applications, calculate hydrostatic pressure from height and specific gravity — then take it into the DP level tools for transmitter ranging.

Frequently asked questions

What is the difference between barg and bara?

Gauge pressure (barg) is measured relative to atmospheric pressure; absolute (bara) is measured relative to a perfect vacuum. They differ by about 1.013 bar at sea level, so 9 barg equals roughly 10.01 bara.

How much pressure does a column of water produce?

About 9.807 kPa per metre of height, or roughly 0.098 bar per metre, for water at standard gravity. Multiply by specific gravity for other liquids.

All calculators are provided for reference and education. Verify independently before use in safety-critical work — see our disclaimer.