Bar to PSI

The bar is the pressure unit on European tire placards, pressure washers, espresso machines and scuba equipment. It is exactly 100,000 pascals, as noted in the SI Brochure. Psi, a pound-force per square inch, is exactly 6894.757293168 Pa by the NIST SP 811 definition. Dividing gives 1 bar = 14.503774 psi, so psi = bar × 14.5038.

Worked examples: a 2.2 bar tire is 31.91 psi; a 150 bar pressure washer is 2,175.6 psi; a 200 bar scuba cylinder is 2,900.8 psi; a 3 bar water mains pressure is 43.51 psi. Millibars, used in weather maps, are a thousandth of a bar, so 1013 mbar is 14.69 psi.

Pressure readings can be gauge (above atmospheric) or absolute. A tire at 2.2 bar on the gauge is about 3.2 bar absolute. Converting between bar and psi does not change which kind of reading you have. The standard atmosphere, 101,325 Pa, equals 1.01325 bar or 14.696 psi; the full converter also has kPa, atm and mmHg.