psi to bar

Tire pressure is the everyday use case: a car's doorjamb sticker may list the recommended pressure in psi, kPa, or bar depending on where the vehicle was built, and a pressure gauge calibrated in the other unit needs converting before trusting the reading, and over- or under-inflating a tire by even a few psi can noticeably change handling and tire wear.

Home espresso machines bring up this pair in a very different setting: European manufacturers almost universally rate their pumps in bar (a "9-bar" pump is the industry standard reference point), while some US gauges, recipes, and modification guides reference psi instead. A home barista comparing a machine's bar rating against a psi-based gauge or mod needs this conversion to make sense of either number, especially when troubleshooting a shot that's pulling too fast or too slow.

To convert pounds-force per square inch to bar, multiply by 0.06894757293:

bar = psi × 0.06894757293

A low-pressure gauge reading of 15 psi equals about 1.03 bar. A typical car tire at 32 psi converts to roughly 2.21 bar. A full aluminum scuba tank rated at 3,000 psi works out to about 206.84 bar.

The factor carries a long decimal because psi is built from the pound-force (defined via a 453.59237-gram pound) and the inch (defined via 0.0254 meter), neither of which lines up neatly with the metric bar. Two decimal places is plenty for tire or compressor gauges, which rarely display more precision than that anyway.

The common mistake is treating bar and standard atmosphere (atm) as the same thing. They're close — 1 bar is about 0.9869 atm — but not identical, and that small gap can matter in lab or industrial settings where a precise pressure setting is required.

A high-pressure industrial hydraulic line rated at 5,000 psi converts to about 344.74 bar, a figure worth keeping in whole numbers given that most hydraulic gauges display pressure in single-digit precision at that scale anyway, and fine-grained decimals add little real-world value at those levels.