Formula
1 Pa = 1 N/m²1 bar = 100,000 Pa = 100 kPa1 atm = 101,325 Pa (exact)1 psi ≈ 6,894.757 Pa1 mmHg ≈ 133.322 Pa How it works
Pressure is force per unit area. The SI unit, the pascal, is one newton per square meter — a tiny amount, so kilopascals are used for most practical figures. The bar (100 kPa) is close to atmospheric pressure at sea level and is popular in Europe for tires and scuba tanks.
In the US, tire and air-compressor pressures are usually given in psi (pounds-force per square inch). A typical passenger-car tire at 32–35 psi is about 2.2–2.4 bar. These are gauge pressures — the amount above the surrounding air.
The standard atmosphere is defined as exactly 101,325 Pa. Blood pressure is still measured in millimeters of mercury, an old unit based on how high air pressure pushes a column of mercury: one atmosphere supports 760 mm.
Frequently asked questions
What is 2.5 bar in psi?
About 36.3 psi.
What is the difference between psi and psig?
psig is gauge pressure (relative to the air around you) and psia is absolute pressure (relative to a vacuum). psia = psig + about 14.7 at sea level. The conversion factors are the same for both.