Convertisseur de pression

One standard atmosphere (atm) equals 101,325 Pascals, while one bar equals exactly 100,000 Pascals. The difference is about 1.3%. The atmosphere is defined by the average air pressure at sea level, while the bar was created as a convenient round number close to atmospheric pressure. In practice, 1 bar and 1 atm are often used interchangeably for rough estimates, but the distinction matters in precise scientific and engineering calculations.

Torr and millimeters of mercury (mmHg) are nearly identical units. One torr is defined as exactly 1/760 of a standard atmosphere (133.322 Pa), while 1 mmHg is based on the pressure exerted by a 1mm column of mercury under standard gravity (133.322 Pa). The difference between them is negligible for all practical purposes. Both units are widely used in medicine for blood pressure readings and in vacuum science.

PSI (pounds per square inch) is the standard pressure unit in the US customary system and is used throughout the United States for tire pressure, compressed gas systems, and hydraulic equipment. It measures force in pounds-force applied per square inch of area. Most US tire pressure gauges read in psi, with typical car tires at 30-35 psi, bicycle tires at 80-130 psi, and truck tires at 80-100 psi. In metric countries, bar or kPa are used instead.

A technical atmosphere (at) equals the pressure of one kilogram-force per square centimeter (98,066.5 Pa). It differs from a standard atmosphere (101,325 Pa) by about 3.2%. The technical atmosphere was commonly used in older European engineering specifications, particularly in Germany and Russia, before being largely replaced by the bar and Pascal in modern practice. You may still encounter it in legacy equipment documentation and some industrial standards.