The physical quantity "pressure" (p) describes the effect of a force (F) on an area (A):

p = F / A

The unit of pressure is the Pascal (Pa). 1 Pa = 1 N / m²

The unit bar is also valid: 1 bar = 105 Pa

The units are no longer valid

• atm: physical atmosphere 1 atm = 106 dyn/cm² = 101325 Pa
• at: technical atmosphere 1 at = 1 kp / cm² = 104 kp/m² =
• atü: technical atmosphere overpressure 1 atü =2 at
• Torr: 1 Torr = 1/760 atm = 101325/760 Pa

The Torr is the unit for millimeters of mercury (mmHg). One Torr is the pressure generated by a mercury column 1mm high.

The unit mmHg, on the other hand, is still a legal unit that can be used for blood pressure and the pressure of other body fluids.

In the USA, Torr and psi (pound per square inch) are the common units for pressure. Tire pressure, for example, is given in psi.

1 psi = 1 lbf/in² = 1 lb · 9.80665 m/s² / in² = 6894.75 Pa = 0.068948 bar = 68.9475

1 bar = 14.504 psi

The unit "meter of water column" is no longer permitted. It is used primarily in organ building, for information on the tightness of tent fabrics, and for medical ventilators.

https://de.wikipedia.org/wiki/Wasserdichtigkeit

The pressure of 1 meter of water column corresponds to one megapond per square meter.

1000 kg 9.80665 m/s² / m² =  9806.65 N/m² = 9806.65 Pa