PSI and bar — two units, one measurement
Pressure is the same physical quantity whether you read it in PSI or bar. The difference is purely historical: PSI (pounds per square inch) is the imperial unit dominant in the United States, and bar is the metric unit widely used in Europe, scientific contexts, and international industry. Converting between them is a single multiplication or division, but knowing which value to expect in which context saves a lot of confusion.
The quickest way to convert is the Pressure Converter, which shows PSI, bar, and nine other units at once for any value you enter. This guide explains the conversion and when each unit is used.
The conversion factor
The exact relationship is:
- 1 bar = 14.5037738 PSI
- 1 PSI = 0.0689476 bar
For everyday use, the approximation 1 bar ≈ 14.5 PSI is accurate enough. Going the other direction, divide your PSI value by 14.5 to get bar.
| PSI | Bar |
|---|---|
| 15 | 1.03 |
| 20 | 1.38 |
| 25 | 1.72 |
| 30 | 2.07 |
| 32 | 2.21 |
| 35 | 2.41 |
| 40 | 2.76 |
| 45 | 3.10 |
| 60 | 4.14 |
| 100 | 6.89 |
Car and motorcycle tyre pressures
Tyre pressure is the most common everyday use of PSI-to-bar conversion. Most passenger cars in the US list recommended pressures in PSI (typically 30–35 PSI), while European specifications and many tyre gauges sold internationally display bar (typically 2.0–2.5 bar). The values below cover most passenger vehicles:
| Vehicle type | Typical PSI | Typical bar |
|---|---|---|
| Compact car (front/rear) | 30–33 | 2.07–2.28 |
| Saloon/SUV | 32–36 | 2.21–2.48 |
| Light truck | 35–45 | 2.41–3.10 |
| Motorcycle (front) | 28–36 | 1.93–2.48 |
| Motorcycle (rear) | 32–42 | 2.21–2.90 |
Always use your vehicle’s door-placard or owner’s manual value rather than the maximum printed on the tyre sidewall. The sidewall figure is the maximum the tyre can safely hold, not the recommended operating pressure. Use the Pressure Converter to cross-check if your gauge reads in different units to the placard.
Bicycle tyre pressures
Bicycle pressures vary dramatically by tyre type and are almost always stated in both PSI and bar:
| Tyre type | Typical range |
|---|---|
| Road (narrow, 23–28mm) | 80–120 PSI (5.5–8.3 bar) |
| Gravel / touring | 40–70 PSI (2.8–4.8 bar) |
| Mountain (hardtail) | 25–40 PSI (1.7–2.8 bar) |
| Mountain (enduro/downhill) | 20–28 PSI (1.4–1.9 bar) |
| Fat bike | 5–15 PSI (0.35–1.0 bar) |
Tubeless tyres typically run 10–15 PSI lower than tubed equivalents.
Diving — working with bar and PSI
Scuba diving universally uses bar for measuring cylinder pressure in most of the world; PSI is used in the United States. A full aluminium 80 scintillating cylinder holds 3,000 PSI (about 207 bar). A steel 12-litre cylinder is typically filled to 200–230 bar (2,900–3,336 PSI). Dive computers and regulators from European manufacturers display bar; US regulators display PSI. Converting between them is critical for safe dive planning: the Pressure Converter handles the conversion to whatever unit your gauges display.
Industrial and engineering contexts
In industrial settings, you encounter a mix of units depending on the origin of the equipment:
- Hydraulic systems: commonly rated in bar (European) or PSI (US). A hydraulic line at 200 bar is about 2,900 PSI.
- Air compressors: a typical workshop compressor delivers 7–10 bar (100–145 PSI).
- Boilers: low-pressure steam systems run at 1–10 bar; high-pressure power generation at 100+ bar (1,450+ PSI).
- Pipe fittings: pressure ratings may appear in bar or PSI on the same data sheet depending on the standard used.
When working from a European drawing or datasheet in a US workshop (or vice versa), always convert before setting pressures. A misread of bar as PSI results in a pressure seven times too high — a potentially dangerous error.
A quick method without a tool
When you need a fast mental approximation and don’t have the Pressure Converter to hand:
- PSI → bar: divide by 15 (result is slightly high, actual factor is ÷14.5).
- bar → PSI: multiply by 15 (result is slightly high, actual factor is ×14.5).
For safety-critical applications, always use the exact factor of 14.5038.
Summary
1 bar equals 14.5038 PSI. Car tyres in the US are typically 30–35 PSI (2.0–2.4 bar); in Europe they are stated in bar. Bicycle road tyres run up to 120 PSI (8.3 bar); mountain tyres run as low as 20 PSI. Diving cylinders use bar worldwide except the US. For an instant, exact conversion between PSI, bar, and nine other pressure units, use the Pressure Converter.