Bar vs PSI and How to Convert Between Them

Bar and psi both measure pressure: a force spread over an area. The bar is a metric unit used across Europe and in much of the world. The psi, short for pound-force per square inch, is the US customary unit.

Both show up on tire gauges, air compressors, pumps and hydraulic equipment. Many gauges print both scales on the same dial.

• One bar is exactly 100,000 pascals (Pa), which is 100 kPa. It is not an SI unit, but it is defined directly from the pascal.
• One psi is the pressure of one pound-force (exactly 4.4482216152605 N) acting on one square inch (exactly 0.0254 m × 0.0254 m).
• From these definitions, 1 psi ≈ 6894.7573 Pa and 1 bar ≈ 14.503774 psi.

One bar is close to, but not equal to, atmospheric pressure at sea level. The standard atmosphere is exactly 101,325 Pa, which is 1.01325 bar or about 14.6959 psi.

• Bar to psi: multiply by about 14.50377. Example: 2.5 bar is 36.259 psi.
• Psi to bar: multiply by about 0.06894757, or divide by 14.50377. Example: 32 psi is 2.206 bar.
• Psi to kilopascals: multiply by about 6.894757. Example: 32 psi is 220.6 kPa.

The rows below are typical examples, not recommendations. Always use the pressure printed on your vehicle placard, tire sidewall or equipment manual.

Many passenger car tires are inflated to somewhere around 30 to 35 psi, about 2.1 to 2.4 bar, but the correct value depends on the vehicle and load. Bicycle tires vary much more: road bike tires often run at higher pressures than car tires, while mountain bike tires often run lower. Bike tire sidewalls and pumps commonly show both psi and bar.

Most gauges read gauge pressure: the pressure above the surrounding air. A flat tire reads zero on a tire gauge, even though the air inside is still at atmospheric pressure. Absolute pressure is measured from a perfect vacuum instead.

• psig: pounds per square inch, gauge. This is what tire gauges and compressor gauges show.
• psia: pounds per square inch, absolute. Used in thermodynamics, aviation and process engineering.
• barg and bara: the same distinction for bar, common in industrial specifications.

To go from gauge to absolute, add the local atmospheric pressure. At sea level that is about 1.013 bar or 14.7 psi, and it is lower at altitude. The unit conversion itself is the same for gauge and absolute values: 1 barg converts to about 14.5 psig.

To estimate in your head, use 1 bar ≈ 14.5 psi. Multiply bar by 14.5 to get psi, or divide psi by 14.5 to get bar. The shortcut is very close to the exact factor of 14.503774, so it is good enough for tires and tools.

An even rougher check: 1 bar is about 15 psi, and 1 psi is about 0.07 bar. Use the converter when you need more than two or three digits.

• Treating 1 bar as exactly one atmosphere. One atmosphere is 1.01325 bar, a small difference that still matters in precise work.
• Mixing gauge and absolute readings. At sea level, a value in psia is about 14.7 higher than the same pressure in psig.
• Reading the wrong scale on a dual gauge. A tire at 2.2 on the bar scale is far from 2.2 psi.