Pressure Units Explained: Pa, kPa, MPa, bar and psi
A practical explanation of common pressure units and what to check before converting engineering or equipment values.
Usefulia · General · Updated
Pascal is the SI pressure unit
One pascal is one newton of force applied over one square metre. Because a pascal is small for many practical applications, technical documents commonly use kilopascals (kPa) and megapascals (MPa).
The metric prefixes are important: 1 kPa is 1,000 Pa and 1 MPa is 1,000,000 Pa.
bar and psi are common outside pure SI notation
Bar is widely used in industrial equipment, pneumatics and gauges. One bar equals 100 kPa, so 10 bar equals 1 MPa.
PSI means pounds per square inch and is common in automotive, compressed-air and US engineering contexts. It uses a different scale and should be converted rather than treated as interchangeable with bar.
Unit conversion is not the same as changing the pressure reference
A converter changes the numerical unit scale only. It does not automatically convert gauge pressure to absolute pressure, because that requires knowing the reference pressure.
When working from a specification, note both the unit and whether the value is gauge, absolute or differential pressure. For safety-critical equipment, verify the original specification and instrument range.