Convert pressure units between units, using exact SI factors.
One bar is 14.504 PSI. A bar is exactly 100,000 pascals, and the pascal is the SI unit of pressure, defined in the BIPM brochure as one newton per square metre. Tyre pressure in Latvia is usually given in bar, while many compressors and gauges read in PSI.
The manufacturer's figure is on a sticker in the door frame or inside the fuel flap, and is usually 2.0–2.5 bar, or 29–36 PSI. It applies to cold tyres; driving raises the pressure by about 0.2 bar, and that rise should not be let out.
A standard atmosphere is 101,325 pascals — average air pressure at sea level. It is not an SI unit, and the BIPM brochure lists it separately from SI, though technical writing still uses it. In practice one atmosphere is nearly one bar; the gap is 1.3%.
Because a hectopascal is numerically identical to the millibar meteorology used for decades, while also being an SI unit with a prefix from the BIPM brochure. The switch therefore changed no numbers at all: 1,013 millibars is 1,013 hectopascals.