PSI to Bar Converter

Multiply bar by about 14.5038. A European tire gauge reading of 2.3 bar is about 33.4 psi, and 1 bar is roughly 14.5 psi. Going the other way, divide psi by 14.5038: a 30 psi tire is just over 2 bar. The displayed factor is rounded, so results are approximations at the shown precision. The conversion is linear with no offset because both units measure the same physical quantity from a true-zero baseline.

1 atmosphere equals exactly 101,325 Pa, 1.01325 bar, and 14.6959 psi. This is the standard sea-level barometric pressure defined by the 10th General Conference on Weights and Measures in 1954, the reference all altimeter and weather measurements use. Inflating a tire to 30 psi means you have added about 30 psi above the surrounding 14.7 psi atmosphere, for an absolute pressure of about 44.7 psi inside the tire.

Psi rules the US (tires, plumbing, air compressors, hydraulics). Bar dominates European automotive and industrial work (most EU tire gauges, pneumatic equipment, espresso machines at 9 bar). Pascals (Pa, kPa, MPa) are the SI unit and the standard in scientific publishing, weather forecasts (hectopascals, 1 hPa = 1 mbar), and engineering specifications worldwide. Atm is the everyday unit in chemistry, especially for gas-law problems. MmHg stays the medical and meteorological standard for blood pressure and barometric pressure (120/80 mmHg blood pressure, 760 mmHg sea-level atmosphere). InHg is used in US aviation for altimeter settings and US weather broadcasts.

Gauge pressure is the pressure above local atmospheric. Absolute pressure includes the 1 atm baseline. A tire gauge reading 32 psi (gauge) means 32 psi above the surrounding 14.7 psi atmosphere, so the absolute pressure inside the tire is about 46.7 psi. Most consumer measurements (tire gauges, blood pressure cuffs, boiler gauges) are gauge pressure. Scientific work usually states absolute pressure explicitly. This converter is unit-agnostic about gauge vs absolute: it converts whatever you enter from one scale to another without adding or subtracting 1 atm.

Tire pressure rises about 1 psi for every 10 deg F (about 0.07 bar per 5 deg C) increase in air temperature, because the gas inside heats up as the tire flexes during driving. The placard inside your driver's door always lists the cold inflation pressure, which is the value to set first thing in the morning or after the car has sat for a few hours. If you check at a highway gas station after an hour of driving and the gauge reads 35 psi, the cold pressure is probably closer to 30 to 32 psi. Setting pressure when the tires are hot leaves you under-inflated once they cool, which hurts fuel economy and tread wear.