Units of Measurement for Pressure

The standard atmosphere, a unit of pressure defined as 101325 Pascals (Pa), is approximately equal to Earth's average atmospheric pressure at sea level. It is denoted by atm.

Bar is a metric unit of pressure. But it is not part of the International System of Units (SI). It is defined as exactly equal to 100,000 Pascals (Pa).

Pascals or kilopascals is a unit of pressure in the International System of Units (SI). Pascal was named in honour of the French mathematician-physicist Blaise Pascal. Pascals are abbreviated to Pa and kilopascals are abbreviated to kPa.

A millimeter of mercury is a manometric unit of pressure, defined as exactly 133.322387415 pascals. It is denoted by mmHg or mm Hg.

The pound per square inch or pound-force per square inch is a unit of pressure based on avoirdupois units (a.k.a a measurement system of weights that uses pounds and ounces as units). It is the pressure resulting from a force of one pound-force applied to an area of one square inch. In the International System of Units (SI), 1 psi is approximately equal to 6894.757 Pa.