Pressure Unit Converter

Convert between pascal (Pa, hPa, kPa, MPa, GPa), bar and millibar (the meteorology standard), the standard atmosphere (atm, 101,325 Pa exactly) and technical atmosphere (at, 1 kgf/cm²), psi (pound per square inch), the mercury columns (mmHg, cmHg, inHg, and the IUPAC-strict Torr), and the water columns (mmH&sub2;O, inH&sub2;O). 16 units with NIST SP 811 and IUPAC factors, round-trip stable. Type a value, pick a source unit, see every other unit at the same instant. Nothing leaves your browser.

About the units
  • Pa, hPa, kPa, MPa, GPa — SI prefixes of the pascal. The pascal is a derived SI unit, one newton per square metre.
  • mbar, bar — the bar (1 bar = 100,000 Pa exactly, CIPM / ISO 80000-4) is the canonical engineering pressure; millibar is the meteorology standard (weather maps use hPa and mbar interchangeably, 1 hPa = 1 mbar).
  • atm — standard atmosphere, exactly 101,325 Pa (IUPAC 1982, NIST). The IUPAC-strict Torr is defined as 1 atm / 760.
  • at — technical atmosphere, exactly 1 kgf/cm² = 98,066.5 Pa. Found on older European pressure-gauge nameplates and diving tables.
  • psi — pound-force per square inch, 1 psi = 6,894.757293168361 Pa (NIST SP 811). The North American industrial / tyre-pressure standard.
  • mmHg, cmHg, inHg — columns of mercury under standard gravity. The conventional mmHg (CIPM) is 133.322387415 Pa; this is what clinical sphygmomanometers and barometers use.
  • Torr — the IUPAC-strict unit, 1 Torr = 101,325 / 760 Pa. Differs from the conventional mmHg by about 0.019 Pa (the gap is meaningful at sub-ppm vacuum work, negligible in clinical practice).
  • mmH&sub2;O, inH&sub2;O — columns of water under standard gravity. Used in low-pressure HVAC / duct work and medical ventilator circuits.

Not shipped: gauge vs absolute pressure (the conversion is identical; the difference is a measurement basis, not a unit). Conversion is round-trip stable to within 1 ULP of IEEE-754 precision.