Pressure converter

The pascal, one newton of force spread over one square meter, is the SI reference unit for pressure, and every unit here converts back to it. A bar is 100,000 Pa, a standard atmosphere is 101,325 Pa, and a pound-force per square inch (psi) is 6,894.757293168361 Pa — figures that look arbitrary until you remember they're each anchored to a different real-world reference: sea-level air pressure, a column of mercury, a force per unit area in imperial units, and so on.

The default pairing is bar to psi. Multiply by 14.50377377 to go from bar to pound-force per square inch:

psi = bar × 14.50377377

Reverse it by multiplying by 0.06894757293, the same as dividing by 14.50377377. A car tire inflated to 2.2 bar reads 2.2 × 14.50377377 = 31.91 psi on a US gauge, and one standard atmosphere, by definition 101,325 Pa, works out to about 14.70 psi.

Pressure units cluster by field almost as sharply as any category on this site. Meteorologists report barometric pressure in hectopascals or millibars (the two are numerically identical). Medicine measures blood pressure in millimeters of mercury (mmHg) purely by historical convention, long after mercury column gauges stopped being the instrument of choice. Divers and anyone working with compressed gas think in bar or atmospheres. US automotive, HVAC, and hydraulic work runs on psi, while structural and aerospace engineering increasingly uses pascals and kilopascals to match international standards.

A subtle point of confusion: Torr and millimeters of mercury are often treated as identical, and for almost every practical purpose they are, but they're not defined the same way. A Torr is defined as exactly 1/760 of a standard atmosphere (133.3223684... Pa), while mmHg is defined from the physical weight of an actual mercury column under standard gravity (133.322387415 Pa) — a difference of about two parts in a million, invisible in daily use but a real distinction in high-precision metrology. Mixing up gauge pressure (relative to atmospheric) and absolute pressure is a separate, more consequential trap, though this page converts magnitudes rather than gauge-versus-absolute readings.