Reckoning / Measure / Pressure
Measure · 8 units
Pressure
Pressure is force per area; the pascal is 1 N/m². Weather maps use hectopascals (equal to millibars), medicine uses millimetres of mercury, and tyre gauges in the US use pounds per square inch.
Convert pressure
Then and now
Mercury columns gave the old units their names: the torr and the conventional millimetre of mercury differ by about one part in seven million.
All pressure units
“Exact” means the unit is defined as an exact multiple of the SI unit; the decimal is printed in full when it ends. Rows marked historical or obsolete are kept for reading old documents.
| Unit | Defined as | In SI | Status | Source |
|---|---|---|---|---|
| SI | ||||
| pascal Pa | 1 N/m² | 1 Pa | exact | BIPM SI Brochure |
| kilopascal kPa | 1000 Pa | 1 000 Pa | exact | BIPM SI Brochure |
| Metric | ||||
| bar bar | 100 000 Pa | 100 000 Pa | exact | BIPM SI Brochure |
| Medicine | ||||
| millimetre of mercury mmHg | 133.322 387 415 Pa (conventional) | 133.322 387 415 Pa | exact Still used for blood pressure. It differs from the torr in the seventh figure. | NIST SP 811 |
| Aviation / weather | ||||
| inch of mercury inHg | 25.4 conventional millimetres of mercury | 3 386.388 640 341 Pa | exact | NIST SP 811 |
| US engineering | ||||
| pound per square inch psi | 1 pound-force on 1 square inch | 6 894.757 293 17… Pa | exact | NIST SP 811 |
| Conventional | ||||
| torr Torr | 1/760 standard atmosphere | 133.322 368 421… Pa | exact | NIST SP 811 |
| standard atmosphere atm | exactly 101 325 Pa | 101 325 Pa | exact | NIST SP 811 |