Tyres, gauges and technical datasheets
Convert bar to psi for tyre pressure, kPa for technical specs or mmHg for medical readings. Exact factors for garage and lab alike.
Tyre placards are the most common reason people need this: European cars list bar, American gauges read psi, and the two are not close enough to eyeball.
One bar is 14.5 psi. Getting that backwards is how tyres end up dangerously under-inflated, so the direction of the conversion matters as much as the number.
The converted pressure across pascals, kPa, bar, psi, atmospheres and mmHg Tyre-friendly bar and psi conversion in both directions mmHg for blood pressure and vacuum measurements One standard atmosphere is 101,325 Pa by definition. Tyre gauges read pressure above the surrounding air, not absolute pressure — the placard figure is what you match. How many psi is 2 bar? 29 psi. Most family cars want somewhere between 2.0 and 2.5 bar, which is roughly 29 to 36 psi.
Is a bar the same as an atmosphere? Nearly. A bar is 100,000 Pa and an atmosphere is 101,325 Pa, so an atmosphere is about 1.3% higher. Close enough for tyres, not for calibration.
Why is blood pressure measured in mmHg? Early instruments balanced pressure against a column of mercury and the reading was literally its height in millimetres. The mercury is long gone; the unit stayed.
Should I check tyres warm or cold? Cold. Driving heats the air and can add 3 to 4 psi, so a warm reading will tell you the tyre is fine when it is not.
Worked example A European tyre placard
Input: 2.2 bar → psi
Output: 31.9 psi
Note: Round to 32 psi on a garage gauge. Setting 22 psi by mistake would leave the tyre badly under-inflated.
