Pressure is defined as force per unit area applied to an object in a direction perpendicular to the surface.
The table below presents conversion factors between common units of force.
Standard units = Pascal (P)
| | atmosphere | inch of water | lb per sq in | lb per sq ft | cm of Hg | dyn/cm2 | pascal |
| 1 atm = | 1 | 406.8 | 14.70 | 2116 | 75.99 | 1.013 * 106 | 1.013 * 105 |
| 1 in water = | 2.458 * 10-3 | 1 | 3.613 * 10-2 | 5.202 | 0.1868 | 2491 | 249.1 |
| 1 lb/in2 = | 6.805 * 10-2 | 27.68 | 1 | 144 | 5.171 | 6.895 * 104 | 6.895 * 103 |
| 1 lb/ft2 = | 4.725 * 10-4 | 0.1922 | 6.944 * 10-3 | 1 | 3.591x10-2 | 478.8 | 47.88 |
| 1 cm Hg = | 1.316 * 10-2 | 5.353 | 0.1934 | 27.85 | 1 | 1.333 * 104 | 1333 |
| 1 dyn/cm2 = | 9.869 * 10-7 | 4.015 * 10-4 | 1.450 * 10-5 | 2.089 * 10-3 | 7.501 * 10-5 | 1 | 0.1 |
| 1 Pa = | 9.869 * 10-6 | 4.015 * 10-3 | 1.450 * 10-4 | 2.089 * 10-2 | 7.501 * 10-4 | 10 | 1 |
| in of water @ 4º C | 1 bar = 106 dyn/cm2 |
| cm of Hg @ 0º C | 1 atm = 29.92 in of Hg |