There are numerous units used to measure pressure…
| Pressure Units | Name | Comparison to 1 atm |
| psi | Pounds per square inch | 14.7 psi |
| Pa | Pascal | 101325 Pa |
| mmHg Torr* | Millimeters of mercury Torr | 760 mmHg or Torr |
| inH2O | Inches of water | 407.2 inH2O |
| atm | Atmosphere | 1 atm |
Gauge versus Absolute Pressure
Imagine that you were swimming in the ocean. You would feel more pressure on your body as you go farther down. At some point, you would not be able to survive without a special pressurized suit. The same is true even though you are standing on the beach beside the ocean. You are standing at the very bottom of a sea of air, and there is pressure with all that air. The reason that you don’t feel anything is simply because you are accustomed to it. You are not crushed because your body’s contents are pushing out with the same pressure as the air. This is considered to have a gauge pressure of zero or 0 psig. If you dive back into the ocean, your gauge reading will increase as you go down. If you add the atmospheric pressure and the gauge reading, you get the absolute pressure.