The formula
Pa = atm × 101,325
Where the factor comes from — each unit by its definition, then its size in SI:
1 atm = (standard atmosphere in Pa, CODATA 2022) × Pa = 101,325 Pa1 Pa is the SI unit of pressure.
Dividing the two SI sizes gives the factor: 101,325, exact — every step above is a definition, not a measurement. The reverse factor is 9.86923266716 × 10⁻⁶.
Pressure is force per area; the pascal is one newton per square metre. Tyres are quoted in psi or bar, weather in hPa, blood pressure in mmHg and gas laws in pascals or atmospheres.
Worked examples
- A car tyre (US gauge) (32 psi): 2.17747 atm = 220,632 Pa — 2.17747 × 101,325 = 220,632
- Sea-level air: 1 atm = 101,325 Pa — 1 × 101,325 = 101,325
- A car tyre (European gauge) (2.2 bar): 2.17123 atm = 220,000 Pa — 2.17123 × 101,325 = 220,000
- A systolic blood-pressure reading (120 mmHg): 0.157895 atm = 15,998.7 Pa — 0.157895 × 101,325 = 15,998.7
Frequently asked questions
How many pascals is 1 atm?
1 atm = 101,325 Pa, exactly, from the unit definitions.
How do I convert pascals back to standard atmospheres?
Divide by 101,325 — or multiply by 9.86923266716 × 10⁻⁶: 1 Pa = 9.86923266716 × 10⁻⁶ atm.