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32 psi · 2.21 bar · 221 kPa
220,632 pascals, gauge — that is, above the air around the tyre.
This page converts units. It does not tell you what any tyre should be inflated to, and no number on it is a suggestion. That figure belongs to the vehicle, not to the tyre: look for the placard in the driver’s door aperture, inside the fuel filler flap or in the handbook, and ask a tyre professional if the vehicle is loaded, towing or wearing a size the placard does not list.
The definitions are exact rather than measured, so nothing is lost in the arithmetic. One bar is 100 kilopascals by convention, and one pound-force per square inch is 6894.757293168 pascals, which follows from the pound-force and the square inch both being defined exactly in metric terms. Everything above is one multiplication and one division through pascals.
Every figure here is gauge pressure — the amount by which the inside of the tyre exceeds the atmosphere outside it, which is what a hand gauge and a forecourt air line both read. Absolute pressure adds the atmosphere back on and is roughly one bar higher, so a specification quoted absolute is not the same number as one quoted gauge. Air also expands as it warms, which is why a reading taken after a drive differs from one taken cold, and why placards state the condition the figure applies in.
Pressure is force spread over an area, and the three units in common use around a tyre differ only in which force and which area they were built from. Pounds per square inch is the imperial survivor, still printed on most placards in the United States and on nearly every hand gauge sold anywhere. Bar is the metric workshop unit, sized so that one of them is roughly the pressure of the atmosphere. Kilopascals are the SI answer, and are what a European placard and most vehicle documentation actually state.
This page moves a number between those three scales. It does not tell you what figure to put in a tyre, and it deliberately contains no such figure. That number is a property of the vehicle rather than of the tyre, and it is printed on the placard in the driver’s door aperture, inside the fuel filler flap, or in the handbook.
The conversions carry no uncertainty of their own, because both relationships are defined rather than observed. A bar is exactly 100 kilopascals, which is exactly 100,000 pascals, by convention.
The pound per square inch is exact too, if less tidily: the pound-force is defined as 4.4482216152605 newtons and the square inch as 6.4516 square centimetres, so one psi works out at exactly 6,894.757293168 pascals. Every answer on this page is that constant applied once in each direction, which is why a value converted out and back again returns to itself.
A placard quoting 2.2 bar is quoting 220 kPa, which is 31.9 psi — the sort of arithmetic that matters when a European car meets an American forecourt gauge. Going the other way, 35 psi is 2.41 bar and 241 kPa.
Notice the resolution mismatch. A tenth of a psi is a finer distinction than a whole kilopascal, and bar needs two decimal places to keep pace with either. That is why this tool shows different numbers of decimals on different scales: rounding bar to one decimal throws away detail the other two units are still carrying.
Every figure here is gauge pressure: the amount by which the inside of the tyre exceeds the air outside it. That is what a forecourt air line and a pencil gauge both read, and it is what a placard states. Absolute pressure adds the surrounding atmosphere back on and comes out roughly one bar higher, so a specification quoted in absolute terms is not the same number as the same specification quoted as gauge.
Temperature moves the reading as well. Air warms as a tyre flexes on a drive and the pressure inside rises with it, so a reading taken at the roadside after an hour differs from one taken in the morning, on the same tyre, with nothing having changed but the temperature. This is why placards specify the condition their figures apply in, and why a conversion tool cannot substitute for reading one.
Close, but not identical. The standard atmosphere is defined as exactly 101,325 pascals, while the bar is defined as exactly 100,000, so an atmosphere is about 1.3% larger. The difference rarely matters at a tyre valve, but it matters a great deal in a laboratory specification, so the two names are not interchangeable.
An older metric unit still found on workshop gauges and some Japanese equipment. The kilogram-force is defined as exactly 9.80665 newtons, so one kgf/cm² is 98.0665 kPa — about 2% under a bar. Many gauges marked this way are also marked in bar, and the two scales are close enough that people confuse them.
Instrument tolerance, mostly. Cheap gauges drift, forecourt lines take abuse, and the act of pressing a gauge onto a valve releases a small amount of air before it seals. Temperature accounts for the rest. Trust one gauge you have reason to believe, and check it against another occasionally rather than averaging them.
No, and that is deliberate. Nothing derivable from a tyre size, a wheel diameter or a unit conversion can produce that figure — it comes from the vehicle placard or handbook, and from a tyre professional when the vehicle is loaded, towing, or wearing a size the placard does not list.