Your car's door placard says psi, the pump at a European garage shows bar, a lot of modern gauges show kPa - same pressure, three different numbers.
| psi | bar | kPa |
|---|---|---|
| 30 | 2.07 | 206.8 |
| 32 | 2.21 | 220.6 |
| 35 | 2.41 | 241.3 |
| 38 | 2.62 | 262.0 |
Most passenger cars run 30-35 psi (about 2.1-2.4 bar / 207-241 kPa); SUVs and light trucks often run higher, 35-44 psi. Always use the pressure on your vehicle's door placard or owner's manual, not the maximum figure printed on the tire sidewall - that's the tire's limit, not the recommended setting. Check pressure cold, before driving or after the car has sat for a few hours; driving heats tires and can raise the reading by 4-6 psi, which would give a falsely high number.
A different, related question - how much pressure a weight puts on the surface below it, given the contact area. Useful for load-spreading questions (a crane mat, a tracked vehicle) rather than tire inflation.
A 20-tonne excavator on two wide tracks (3.355m x 0.6m each) puts down about 48.7 kPa of ground pressure - similar to a person walking. The same weight on a small footprint would be dramatically higher: a person standing in narrow stiletto heels can put over 13 MPa on the ground at the point of contact, hundreds of times more than the same person's weight spread across a flat shoe. This is exactly why tracked vehicles use wide tracks instead of narrow wheels on soft ground, and why a crane needs a mat under its outriggers.