Bar to PSI Converter

bar to pounds per square inch — quick reference

The formula, worked line by line

Both units measure force spread over an area, so the conversion is a single multiplication with no offset. A bar is 100,000 pascals by definition. A psi is one pound-force pressing on one square inch, which comes to 6,894.7572931683613... pascals — a figure with no end to it.

Divide one by the other and the digits never stop: 14.5037737730209215… That is worth stating carefully. The conversion IS exact, because every quantity feeding it is defined rather than measured — but it is exact as a fraction, and no decimal you write down will ever be.

psi = bar × 14.5038 (a rounding; the true ratio never terminates)
bar = psi ÷ 14.5038
2.5 bar → 2.5 × 14.5038 = 36.26 psi
And the round one: 1 bar = 100 kPa exactly

Where the wrong shortcuts come from

The ten-times rule is a misfiled memory. One bar really is exactly 100 kilopascals, and that relationship is worth knowing — but kilopascals are not psi, and swapping one for the other understates every pressure by 31%. On a 2.2 bar tyre it suggests 22 psi against a true 31.9.

The fifteen-times rule is closer and still wrong in a way that compounds. It overstates by 3.4%, which is a third of a psi on a car tyre and nearly a hundred psi on a scuba cylinder. Use it to sanity-check an answer, never to produce one.

Only one number in this conversion is truly round, and it is on the metric side: a bar is exactly 100 kilopascals. Bar to psi has no exact decimal at all, so every psi figure you have ever read off a conversion chart was rounded somewhere.

How to use the bar to PSI converter

Type a pressure in bar and the psi equivalent appears as you type. Swap turns the page into a psi to bar converter without retyping, which is the fastest way to read a European gauge against an American placard or the other way round.

Nearly everyone who needs this conversion is standing next to a tyre. A European car quotes its pressures in bar, an American gauge reads in psi, and the two numbers look nothing like each other — which is exactly why the wrong shortcuts are so tempting.

The factor is 14.5038, and every input to it is a definition rather than a measurement: a pound-force is fixed through standard gravity, an inch is exactly 25.4 millimetres, and a bar is exactly 100,000 pascals. Nobody measured this conversion. It was decided.

Google records three versions of the same wrong guess: is one bar ten psi, is three bar thirty psi, is one bar fifteen psi. Ten is 31% low and fifteen is 3.4% high. On a tyre, a 31% error is the difference between a firm tyre and a dangerously soft one.

The ten comes from somewhere real. One bar is exactly 100 kilopascals — the bar was defined that way — so anyone who has met pressure in metric units has seen bar paired with a perfectly round number. That round relationship exists; it just is not the one with psi.

Why your gauge reads zero in open air

A tyre gauge does not measure the pressure inside the tyre. It measures how much higher that pressure is than the air around it, which is why a gauge held in open air reads zero rather than reading the atmosphere pressing on it from every side.

That is called gauge pressure, and every tyre figure you will ever meet is one. Absolute pressure adds the atmosphere back on: at sea level a tyre reading 32 psi on the gauge holds about 46.7 psi absolute, since one standard atmosphere is 14.696 psi.

It matters more than it sounds for anything that is not a tyre. Weather pressure, boiling points and gas-law work are all quoted absolute, while boost gauges, dive computers and air lines are gauge. A number with no label is almost always gauge if a workshop produced it.

Cold pressure, and why the number moves

Air pressure rises as air warms, so a tyre checked after a motorway run reads higher than the same tyre checked in the morning. The placard figure is a cold pressure, meaning the car has been parked for a few hours or driven less than a couple of miles.

Temperature moves it in the other direction too. A tyre loses roughly 0.07 bar, about one psi, for every 5.5 degrees Celsius the air drops, which is why warning lights appear on the first cold morning of autumn without anything having gone wrong with the tyre.

The practical consequence is to set pressures cold and leave a warm tyre alone. Letting air out of a hot tyre to bring it back to the placard figure leaves it underinflated once it cools, which is the opposite of what the adjustment was trying to achieve.

Every bar value, worked out

62 common bar figures each get their own page, with the answer at full precision, the arithmetic, what rounding costs, and the nearest real-world reference point on the scale.

Questions people ask