Tyre pressure turns up in more than one unit, which can make a simple figure look confusing. In fact PSI, bar and kPa are just different scales for the same thing, how hard the air inside is pushing out.
The three units
- PSI: pounds per square inch, the imperial unit, common in the UK and the US, and the one most forecourt gauges default to
- bar: the metric unit used across Europe, and the one many car makers print first on the placard
- kPa: kilopascals, another metric unit seen on some cars and gauges
A typical car pressure of around 32 PSI is about 2.2 bar, or 220 kPa, all the same pressure, written three ways.
Converting between them
The conversions are simple:
- bar to PSI: multiply by about 14.5 (so 2.0 bar ≈ 29 PSI, 2.5 bar ≈ 36 PSI)
- PSI to bar: divide by about 14.5
- bar to kPa: multiply by 100 (1 bar = 100 kPa)
In practice the conversion is rarely needed, because UK pressure placards and most forecourt gauges show both PSI and bar side by side.
The one thing to avoid
The only real pitfall is mixing the scales up, reading a figure in one unit and setting it in another. A car needing 2.2 bar must not be set to 2.2 PSI, which would leave it almost flat. As long as the gauge and the placard are read in the same unit, the numbers look after themselves. When in doubt, match like for like: bar to bar, PSI to PSI. A fitter sets new tyres to the placard figure either way, whether the set comes from a local garage or is bought online from Tyres.co.uk, so the unit only matters when topping up between visits.
From the workshop: the only unit mistakes we see come from someone reading bar off the door and dialling it into a gauge set to PSI. Check which scale the gauge is on first; most have a button to switch.
Sources and accuracy. The unit definitions and conversions here are standard at the time of writing. The car's recommended pressure is the figure that matters, in whichever unit it is given. If anything here looks wrong, get in touch and we will check it and put it right.
Common questions
What is the difference between PSI and bar?+
They are two units for the same thing, air pressure. PSI (pounds per square inch) is the imperial unit common in the UK and US; bar is the metric unit used across Europe. One bar is about 14.5 PSI, so they describe the same pressure in different numbers.
How do I convert bar to PSI?+
Multiply bar by about 14.5 to get PSI, or divide PSI by 14.5 to get bar. So 2 bar is about 29 PSI, and 2.2 bar is about 32 PSI, a typical car pressure. Most placards and forecourt gauges show both, so conversion is rarely needed.
What is kPa on a tyre placard?+
kPa stands for kilopascal, another metric pressure unit. One bar equals 100 kPa, so 2.2 bar is 220 kPa. Some cars and gauges use kPa, but it describes exactly the same pressure as the bar and PSI figures.
Which unit should I use?+
Whichever matches the gauge being used, as long as it is compared against the same unit on the placard. The figures are interchangeable, 32 PSI and 2.2 bar are the same pressure, so the key is not to mix up the numbers between the two scales.