What is a Pound per Square Inch?
PSI (pounds per square inch) is the standard for American tire pressures, hydraulics, and gas-cylinder specifications.
Overview
Pounds per square inch (psi) equals approximately 6,895 pascals and is the standard pressure unit in American tire pressures, hydraulics, and gas-cylinder specifications. American car tires are typically inflated to 30–35 psi, household water systems run at 40–60 psi, and scuba tanks are filled to 3,000 psi (about 200 bar). The psi is essential in American engineering for stress calculations, hydraulic systems, and pneumatic equipment. Two variants exist: 'psig' (gauge, measured above atmospheric) and 'psia' (absolute, including atmosphere) — gauge is the default unless specified. The psi relates to the pascal (1 psi ≈ 6,895 Pa), the kilopascal (1 psi ≈ 6.895 kPa), the bar (14.504 psi = 1 bar), the atmosphere (14.696 psi = 1 atm), and the inch of mercury (1 inHg ≈ 0.491 psi). Outside the US, kPa or bar dominate.
Convert Pound per Square Inch to all units
Live resultRelationship to Other Pressure Units
1 psi equalsVisual reference for how the pound per square inch relates to other pressure units. Each row links to the full converter for that pair.
When Is the Pound per Square Inch Used?
- US tyre pressures
- US plumbing and water system specs
- US compressed-air tool ratings
US tyre: 32–35 psi. Water supply: 40–60 psi. SCUBA tank: 3000 psi. Car AC system: 30–200 psi.
Tips for Using the Pound per Square Inch
- 1 psi ≈ 6.9 kPa = 0.069 bar.
- 14.7 psi = 1 atm = 1.01 bar.
- Most US pressure gauges show psi.
Common Mistakes
- Setting a European tyre at 35 bar instead of 35 psi — disaster.
- Confusing psi (gauge) with psia (absolute).
- Using psi in scientific papers — prefer Pa or MPa.