Pressure Converter
Convert between PSI, bar, atm, Pascal, and mmHg
Pressure conversions are required in mechanical engineering, fluid dynamics, meteorology, medicine, and industrial processes. Tire pressure in the US is given in PSI, European weather reports use hectopascals, hydraulic systems may reference bar, and medical professionals measure blood pressure in mmHg. The wide variety of pressure units across industries makes a reliable converter indispensable. MegaCalc supports all standard pressure units including Pascal, bar, atm, PSI, torr, and mmHg.
Multi-Unit Converter
All conversions for 1 Pa
About Pressure Units
The SI unit of pressure is the Pascal (Pa = N/m²). Practical engineering uses kilopascals (kPa) and megapascals (MPa). Atmospheric pressure units include bar (≈ 1 atm), atmospheres (atm), and mmHg (torr). US engineering commonly uses PSI (pounds per square inch). Meteorology uses hectopascals (hPa) or millibars (mbar).
History of Pressure Measurement
Pressure measurement developed from the study of gases and fluids. Evangelista Torricelli built the first mercury barometer in 1643, measuring atmospheric pressure as the height of a mercury column — the origin of pressure units like mmHg and torr. Blaise Pascal established the mathematical foundations of hydrostatic pressure, and the SI unit is named in his honor. The bar was defined as approximately one atmosphere for meteorological convenience. PSI (pounds per square inch) arose from British and US engineering practice and remains dominant in American industrial and automotive contexts.
Practical Tips for Pressure Conversions
At sea level, 1 atmosphere ≈ 101.3 kPa ≈ 1.013 bar ≈ 14.7 psi ≈ 760 mmHg. When working with tire pressures, note that specifications may include 'cold' pressure which should be measured before driving. For blood pressure, normal adult systolic is around 120 mmHg (about 16 kPa or 2.3 psi). Vacuum gauges may read in 'inches of mercury below atmospheric' rather than absolute pressure, so conversions must account for the reference point.
Common Pitfalls to Avoid
The distinction between gauge pressure (relative to atmospheric) and absolute pressure is the most common source of confusion. A tire gauge reading 32 psi actually has absolute pressure of 46.7 psi. Similarly, vacuum measurements may be reported as negative gauge pressure or positive vacuum pressure. In thermodynamics calculations involving the ideal gas law, always use absolute pressure.
Professional Uses
Mechanical engineers specify pipe and vessel pressures in kPa, MPa, bar, or psi. HVAC technicians work with refrigerant pressures in psi or bar. Scuba divers calculate depth pressures in atmospheres or bar. Meteorologists report atmospheric pressure in hPa or inches of mercury. Medical professionals measure blood pressure in mmHg. Food processing engineers use specific pressure ranges for pasteurization and sterilization.
All Pressure Conversions
From Pascal (Pa)(8 of 11 shown)
From Kilopascal (kPa)(8 of 11 shown)
From Bar (bar)(8 of 11 shown)
From Atmosphere (atm)(8 of 11 shown)
From Pound per Square Inch (psi)(8 of 11 shown)
From Millimeters of Mercury (mmHg)(8 of 11 shown)
Frequently Asked Questions
What is the difference between absolute and gauge pressure?
Absolute pressure is measured relative to a perfect vacuum (zero pressure). Gauge pressure is measured relative to ambient atmospheric pressure. Tire pressure, for example, is gauge pressure — a reading of 35 PSI (gauge) means 35 PSI above atmospheric, which is about 49.7 PSI absolute. MegaCalc converts absolute pressure values; for gauge conversions, add or subtract 1 atm as appropriate.
How many PSI is 1 bar?
1 bar equals 14.5038 PSI. Standard atmospheric pressure is 1.01325 bar, which equals 14.696 PSI.
What is the standard atmosphere in different units?
1 standard atmosphere (atm) = 101,325 Pa = 1.01325 bar = 14.696 PSI = 760 mmHg = 29.92 inHg. This value represents average sea-level atmospheric pressure and is used as a reference point in many calculations.