Pressure Converter

Every Industry Has Its Own Pressure Language

Pressure is the physical quantity with perhaps the most industry-specific unit fragmentation of any common measurement. Tyre fitters in the UK work in PSI or bar. Weather forecasters report in hectopascals (hPa) or millibars. Anaesthesiologists read blood pressure in mmHg. Chemical process engineers design to bar or kPa specifications. Vacuum technology specialists use Torr or millibar. High-pressure equipment manufacturers specify in MPa. Each field arrived at its preferred unit through historical convention, practical instrument ranges, and regional standards — and none of them is going away any time soon. This converter supports all the major pressure units so you can work across disciplines without stopping to look up ratios.

Absolute vs Gauge Pressure — A Critical Distinction

Before converting any pressure value, you need to know whether it is absolute pressure or gauge pressure. Absolute pressure is measured relative to a perfect vacuum (zero). Gauge pressure is measured relative to current atmospheric pressure (approximately 101,325 Pa at sea level). Most everyday instruments — tyre pressure gauges, blood pressure cuffs, bicycle pumps — read gauge pressure. A car tyre inflated to "32 PSI" means 32 PSI above atmospheric, so the absolute pressure inside is roughly 32 + 14.696 = 46.7 PSI absolute. This converter works with absolute pressure values. If your reading came from a gauge instrument, add approximately 1 atm (101,325 Pa / 14.696 PSI / 1.01325 bar) before converting to get absolute values.

Understanding the Pascal and Its Multiples

The pascal (Pa) is the SI unit of pressure, defined as one newton per square metre. It is a very small unit — standard atmospheric pressure is 101,325 Pa — so practical engineering and science typically uses multiples. The kilopascal (kPa) = 1,000 Pa is common in pneumatic systems and weather science. The megapascal (MPa) = 1,000,000 Pa is used for structural engineering, hydraulic systems, and tensile strength specifications. The hectopascal (hPa) = 100 Pa equals exactly 1 millibar and is the unit meteorologists worldwide use for atmospheric pressure. Standard sea-level air pressure is 1,013.25 hPa — a figure you will see on every weather map.

Blood Pressure, Altitude, and mmHg

Millimetres of mercury (mmHg) — also called Torr — originated in the era of mercury manometers, where pressure was read by how high it pushed a column of mercury. One mmHg is the pressure exerted by a 1mm column of mercury at 0°C under standard gravity: 133.322 Pa. Blood pressure is almost universally reported in mmHg worldwide, even in countries that otherwise use metric exclusively. A reading of "120/80 mmHg" means systolic pressure of 120 mmHg (16,000 Pa) and diastolic 80 mmHg (10,666 Pa). The Torr, used in vacuum science, is defined as exactly 1/760 of a standard atmosphere and is numerically nearly identical to mmHg — the difference is less than 0.000015%. For thermodynamic calculations involving pressure and temperature together, the Temperature Converter handles the temperature side.

Bar vs PSI: The Two Dominant Workshop Units

In workshops, garages, and manufacturing floors, the contest is between bar and PSI. The bar (100,000 Pa) was introduced as a near-metric approximation of atmospheric pressure and is the dominant unit in European industry. PSI (pounds per square inch = 6,894.76 Pa) dominates in the US. The conversion factor — 1 bar ≈ 14.5038 PSI — is close enough to 14.5 that rough conversions are easy, but precise enough to matter for safety-critical applications. Tyre pressure for a car might be specified as 2.2 bar (European) or 32 PSI (US) — both describe the same inflation. Compressed air tools typically specify working pressure in bar (6–8 bar) or PSI (87–116 PSI) depending on the manufacturer's market. For fluid volume calculations that accompany pressure work, the Volume Converter is the right complement.

Pressure Conversion Reference

• 1 atm = 101,325 Pa = 1.01325 bar = 14.696 PSI = 760 mmHg = 760 Torr
• 1 bar = 100,000 Pa = 0.986923 atm = 14.5038 PSI = 750.064 mmHg
• 1 PSI = 6,894.76 Pa = 0.0689476 bar = 0.068046 atm = 51.715 mmHg
• 1 kPa = 1,000 Pa = 0.01 bar = 0.145038 PSI = 7.50064 mmHg
• 1 MPa = 1,000,000 Pa = 10 bar = 145.038 PSI