In practice, pressure is measured in several different units. This plethora of units and abbreviations has arisen historically as scientists and engineers working on different subjects (liquids, high-pressure gases, low-pressure gases, weather, etc.) developed what seemed to them the most convenient units. These units continue in use through tradition, so it is necessary to become familiar with converting back and forth between them. TABLE 14.2 gives the basic conversions.
| Unit | Abbreviation | Conversion to 1 atm | Uses |
|---|---|---|---|
| pascal | Pa | 101.3 kPa | SI unit: |
| atmosphere | atm | 1 atm | general |
| millimeters of mercury | mm of Hg | 760 mm of Hg | gases and barometric pressure |
| inches of mercury | in | 29.92 in | barometric pressure in U.S. weather forecasting |
| pounds per square inch | psi | 14.7 psi | engineering and industry |