Pressure Converter
Convert units of pressure — pascals, bar, psi, atm, mmHg, torr and inHg.
1 bar = 14.503774 psi
Popular Pressure Conversions
- Pascal to Pound per Square Inch
- Kilopascal to Pound per Square Inch
- Bar to Pound per Square Inch
- Atmosphere to Pound per Square Inch
- Millimeter of Mercury to Pound per Square Inch
- Torr to Pound per Square Inch
- Inch of Mercury to Pound per Square Inch
- Bar to Pascal
- Bar to Kilopascal
- Bar to Atmosphere
- Bar to Millimeter of Mercury
- Bar to Torr
- Bar to Inch of Mercury
About pressure units
Pressure is the force applied perpendicular to a surface divided by the area over which that force acts. Its SI unit is the pascal (Pa), equal to one newton per square meter — a very small quantity by everyday standards. Standard atmospheric pressure at sea level is 101,325 Pa, which is why weather forecasters prefer hectopascals (hPa) or millibars. Engineers working with pneumatics and hydraulics often use bar or psi (pounds per square inch). Medical and meteorological instruments frequently report in millimeters of mercury (mmHg) or inches of mercury (inHg), a legacy of mercury barometers. Tire pressure in the US is stated in psi; in Europe it is usually bar.
History & origin
The pascal is named after the French mathematician and physicist Blaise Pascal, who in the 1640s demonstrated that atmospheric pressure decreases with altitude using his famous Puy de Dôme experiment. The bar was introduced in meteorology in the early 20th century as a convenient round number close to one atmosphere. The millimeter of mercury dates to Evangelista Torricelli's 1643 mercury barometer — the first instrument to measure atmospheric pressure — and the unit torr was later named in his honour.
Tips
The most consequential distinction in pressure measurement is absolute versus gauge pressure. Absolute pressure is measured from true zero (a perfect vacuum). Gauge pressure is measured from atmospheric pressure — it reads zero at sea level because it ignores the atmosphere we live in. Tire pressure gauges, for instance, read gauge pressure: a 'flat' tire at 0 psi gauge still contains 14.7 psi absolute. Industrial specs that say 'psi' almost always mean psi gauge (psig); verify before substituting values.
Common questions
- What is the difference between psi, bar, and atm?
- All three measure pressure but at different scales. 1 atm (standard atmosphere) = 101,325 Pa ≈ 14.696 psi ≈ 1.01325 bar. The bar is close to 1 atm and is common in European engineering. Psi is used predominantly in the United States. Pascals are the SI unit and appear in physics and structural engineering.
- What is the difference between gauge pressure and absolute pressure?
- Absolute pressure is measured from a perfect vacuum (zero). Gauge pressure is measured from ambient atmospheric pressure, so it reads zero when the system is open to the air. To convert gauge to absolute, add approximately 101,325 Pa (14.696 psi) at sea level. Always check which kind a specification uses before making calculations.