Pressure Converter

What pressure measures

Pressure is force acting on a unit of area. The SI unit is the pascal (Pa), that is one newton per square metre. The pascal is very small, so kPa and MPa are often used.

Main units and where they are used

• Bar (100,000 Pa) – tyre, pump and industrial pressure.
• Atmosphere (atm, 101,325 Pa) – standard sea-level atmospheric pressure.
• psi (6894.76 Pa) – US tyre and compressor readings.
• Millimetre of mercury (mmHg, 133.322 Pa) – blood pressure; hectopascal (hPa) – weather forecasts.

Common pitfalls

It is important to tell absolute pressure (from vacuum) from gauge pressure (relative to the atmosphere). A tyre gauge shows gauge pressure, so a tyre at 2.2 bar has an absolute pressure of about 3.2 bar. Another confusion: bar and atmosphere are very close but not identical: 1 atm = 1.01325 bar. When converting psi to bar remember that 1 bar is about 14.5 psi.