psi
The pound-force per square inch (psi) is the US customary unit of pressure: the force of one pound-force acting on one square inch. It is exact in SI because the pound and the inch are defined exactly.
Symbol: psi
Quantity: pressure, stress and differential pressure (force per unit area)
SI relation: 1 psi = 6894.757293168 Pa (exact)
Derivation: 1 psi = 1 lbf/in² = (0.45359237 kg × 9.80665 m/s²) ÷ (0.0254 m)² = 6894.757293168 Pa
Exact: yes, by definition
History
Its SI value became exact with the 1959 international yard and pound agreement, which fixed the inch at 25.4 mm and the pound at 0.45359237 kg.
Typical uses
- Tyre pressure in the United States (about 30–35 psi for cars)
- Compressed-air systems (90–125 psi)
- Hydraulics (up to 3000–5000 psi)
- Gauge (psig), absolute (psia) and differential (psid) readings
Convert psi to other units
| Conversion | 1 psi equals | Reverse |
|---|---|---|
| psi to pascal | 6894.757293 Pa | pascal to psi |
| psi to kilopascal | 6.894757293 kPa | kilopascal to psi |
| psi to bar | 0.06894757293 bar | bar to psi |
| psi to millimeter of mercury | 51.7149252 mmHg | millimeter of mercury to psi |
| psi to inch of water | 27.67990471 inH₂O | inch of water to psi |
| psi to atmosphere | 0.06804596391 atm | atmosphere to psi |
| psi to megapascal | 0.006894757293 MPa | megapascal to psi |
| psi to millibar | 68.94757293 mbar | millibar to psi |
| psi to torr | 51.71493257 Torr | torr to psi |
| psi to millimeter of water | 703.0695796 mmH₂O | millimeter of water to psi |
| psi to centimeter of water | 70.30695796 cmH₂O | centimeter of water to psi |
| psi to inch of mercury | 2.036020677 inHg | inch of mercury to psi |
| psi to decibar | 0.6894757293 dbar | decibar to psi |
| psi to inch of water (60 °F) | 27.7075924 inH₂O (60 °F) | inch of water (60 °F) to psi |
| psi to barye | 68947.57293 Ba | barye to psi |
Open the Pressure Converter to convert any value between all units.
Sources
- Guide for the Use of the International System of Units (SI), NIST Special Publication 811, 2008 Edition, National Institute of Standards and Technology , Appendix B.8, "pound-force per square inch (psi)".
Last reviewed: . Factors are stored exactly and computed with 50-digit decimal arithmetic. See how we verify conversion factors.
Cite this page
APA
Scientific Converters. (2026, October 15). psi. Retrieved October 17, 2026, from https://scientificconverters.com/units/psi/
IEEE
Scientific Converters, "psi," scientificconverters.com. Accessed: Oct. 17, 2026. [Online]. Available: https://scientificconverters.com/units/psi/