Pressure Units — Pascal, PSI, Bar, ATM Explained
Pressure is everywhere — from your car tyres to the weather forecast to scuba diving. Different industries use different units, which can be confusing. Here's a clear breakdown.
The Main Pressure Units
Pascal (Pa)
The SI unit of pressure. 1 Pa = 1 Newton per square meter. Standard atmospheric pressure is 101,325 Pa. Kilopascal (kPa) is more practical for everyday use.
PSI (Pounds per Square Inch)
The dominant pressure unit in the United States. Car tyre pressure is typically 30–35 PSI. Blood pressure in the US is measured in mmHg but converted from PSI in industrial contexts.
Bar
Used widely in Europe and industry. 1 bar ≈ 1 atmosphere (slightly less). Tyre pressure in Europe is often given in bar (2.2–2.5 bar for car tyres).
Atmosphere (atm)
Defined as standard sea-level atmospheric pressure. 1 atm = 101,325 Pa = 14.696 PSI = 1.01325 bar. Used in chemistry and diving.
Conversion Table
| Pa | kPa | PSI | Bar | ATM |
|---|---|---|---|---|
| 1 | 0.001 | 0.000145 | 0.00001 | 0.00001 |
| 1,000 | 1 | 0.145 | 0.01 | 0.00987 |
| 101,325 | 101.3 | 14.696 | 1.013 | 1 |
| 200,000 | 200 | 29.0 | 2.0 | 1.97 |
Real-World Reference Points
- Atmospheric pressure: 101.3 kPa / 14.7 PSI / 1 bar
- Car tyre pressure: 200–250 kPa / 30–36 PSI / 2.0–2.5 bar
- Bike tyre pressure: 480–690 kPa / 70–100 PSI / 4.8–6.9 bar
- Scuba diving at 10m: 2 atm / 202 kPa / 29.4 PSI
- Blood pressure (systolic): ~16 kPa / 120 mmHg
🚗 Tyre pressure tip: Most car tyres need 30–35 PSI (2.1–2.4 bar / 207–241 kPa). Check your car's door sticker for the exact recommended pressure.