Pressure Converter

Pressure describes the force acting on a given area. The SI base unit is the pascal (Pa), named after the French mathematician Blaise Pascal. One pascal corresponds to a force of 1 newton acting on 1 square metre – a very small unit for everyday use. That is why larger multiples are common: the hectopascal (hPa, 100 Pa) is the standard unit in meteorology for air pressure readings. The kilopascal (kPa, 1,000 Pa) is used in pneumatics and mechanical engineering. The bar (100,000 Pa) is especially common in German-speaking countries for technical pressure readings.

In the English-speaking world, PSI (pound per square inch) is the dominant pressure unit. 1 PSI = 6,894.757 Pa ≈ 0.0689 bar. You encounter PSI every day with tire pressure: American vehicle manuals give tire pressure in PSI, European ones in bar. A typical car tire pressure of 2.2 bar corresponds to about 32 PSI. In medicine, blood pressure is measured in mmHg (millimetres of mercury), which is historically related to the torr: 1 torr ≈ 1 mmHg = 133.322 Pa.

The atmosphere (atm) is a historical unit corresponding to the average air pressure at sea level: 1 atm = 101,325 Pa = 1.01325 bar. In science it is used as a reference for standard conditions. The technical atmosphere (at), by contrast, is defined as 1 kp/cm² = 98,066.5 Pa ≈ 0.981 bar – a slightly different value still found in older mechanical engineering.

In vacuum technology, torr and millibar play an important role. High vacuum means pressures below 0.001 mbar. Vacuum quality affects processes such as semiconductor manufacturing, coating technology and freeze-drying. Air pressure also varies with altitude: at 5,500 m it is only about 500 hPa (50% of sea-level pressure). This matters for mountaineers, pilots and the design of high-pressure systems in aerospace.

When converting pressure units, it is important to distinguish between absolute pressure and relative (gauge) pressure. Absolute pressure is measured from a perfect vacuum as zero, while gauge pressure is measured relative to ambient air pressure. In engineering, gauge pressure is often quoted – a tire pressure of 2.2 bar is a gauge pressure; the absolute pressure inside the tire is about 3.2 bar (2.2 + 1 bar ambient pressure). Our converter works with absolute values.