Convert Pressure Units
Pressure Converter
Pressure Conversion Chart
Key relationships between pressure units. The SI unit is the pascal (Pa).
SI Units
| 1 kPa | = | 1,000 Pa | exact |
| 1 MPa | = | 1,000,000 Pa | exact |
| 1 GPa | = | 1,000,000,000 Pa | exact |
| 1 hPa | = | 100 Pa | exact |
Bar & Atmosphere
| 1 bar | = | 100,000 Pa | exact |
| 1 mbar | = | 100 Pa | exact |
| 1 atm | = | 101,325 Pa | exact |
| 1 at (tech) | = | 98,066.5 Pa | exact |
Imperial & Medical
| 1 psi | = | 6,894.757 Pa | |
| 1 kgf/cm² | = | 98,066.5 Pa | exact |
| 1 mmHg (0°C) | = | 133.322 Pa | |
| 1 torr | = | 101,325/760 Pa | exact |
1 standard atmosphere (atm) is defined as exactly 101,325 Pa by the 10th CGPM (1954). 1 bar is defined as exactly 100,000 Pa. 1 kgf/cm² (technical atmosphere) uses standard gravity (g = 9.80665 m/s², exact). 1 torr = 1/760 atm exactly, while 1 mmHg ≈ 1 torr but depends slightly on mercury density and temperature.
About Pressure Units
Automotive & Industrial
Tire pressure uses psi (US) or bar/kPa (metric). Typical car tires: 30-35 psi (207-241 kPa, 2.1-2.4 bar). Hydraulic systems use MPa or bar. Compressed air systems commonly use psi or bar.
Medical & Laboratory
Blood pressure is measured in mmHg (millimeters of mercury). Normal reading: 120/80 mmHg. Vacuum systems in labs use torr or mbar. 1 torr ≈ 1 mmHg, but torr is defined exactly as 1/760 atm while mmHg depends on mercury density.
Meteorology & Aviation
Atmospheric pressure is reported in hPa (hectopascals) or mbar (identical values: 1 hPa = 1 mbar). Standard sea-level pressure: 1,013.25 hPa = 1 atm. Aviation uses inHg (inches of mercury) in the US and hPa internationally.
Engineering & Process
The pascal (Pa) is the SI unit: 1 Pa = 1 N/m². kPa and MPa are common in engineering specifications. The kgf/cm² (technical atmosphere) is still used in some countries for boilers and pressure vessels. 1 kgf/cm² ≈ 0.9807 bar ≈ 14.22 psi.
Do not confuse gauge pressure with absolute pressure. Gauge pressure reads zero at atmospheric level (tire gauges, blood pressure cuffs). Absolute pressure includes atmospheric pressure: Pabs = Pgauge + Patm. When converting, ensure both values use the same reference.
Popular Pressure Conversions
Bar & PSI
kPa & PSI
Atmosphere & Other
Conversion Charts & Tables
Printable charts and reference tables for pressure conversions:
Frequently Asked Questions
What is the relationship between bar and psi?
1 bar equals approximately 14.5038 psi, and 1 psi equals approximately 0.0689476 bar. This is the most common pressure conversion in global engineering because bar is the standard in Europe and much of the world, while psi dominates in the US and UK.
Why is blood pressure measured in mmHg?
The mercury sphygmomanometer, invented in 1896, measures blood pressure by the height of a mercury column in millimeters. Even though most modern devices are digital, the mmHg unit persists by medical convention. A normal reading of 120/80 means 120 mmHg systolic and 80 mmHg diastolic.
What is the difference between gauge pressure and absolute pressure?
Absolute pressure is measured relative to a perfect vacuum (0 Pa). Gauge pressure is measured relative to atmospheric pressure. For example, a tire at 32 psi (gauge) has an absolute pressure of about 46.7 psi (32 + 14.7 psi). Units like psig (gauge) and psia (absolute) make this distinction explicit.
How do I convert between kPa and bar?
Divide kPa by 100 to get bar, or multiply bar by 100 to get kPa. This is exact: 1 bar = 100 kPa by definition. For example, 250 kPa = 2.5 bar, and 3.5 bar = 350 kPa. This makes kPa-to-bar one of the simplest pressure conversions.
Related Converter Categories
- Volume Converter — Gas law: PV = nRT
- Temperature Converter — Gas law: pressure changes with temperature
