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Convert pascals, bar, psi, atmospheres, and torr. Used in engineering, meteorology, and science.
Pressure is force per unit area. The SI unit is the pascal (Pa), defined as one newton per square metre (N/m²). At everyday scales, the pascal is a small unit: atmospheric pressure at sea level is approximately 101,325 Pa. For this reason, kilopascals (kPa) and megapascals (MPa) are more commonly used in engineering. Tyre pressure, for example, is often expressed in kPa in countries that have adopted SI.
The bar is widely used in hydraulics, gas systems, and weather data. One bar equals exactly 100,000 Pa (100 kPa). Standard atmospheric pressure is 1.01325 bar. Weather stations in Europe often report atmospheric pressure in millibars (mbar), where 1 mbar = 100 Pa. A reading of 1013.25 mbar is standard sea-level pressure.
PSI (pounds per square inch) is the dominant pressure unit in the United States. Car tyre pressure is typically 32-36 psi. Industrial hydraulic systems can operate at several thousand psi. One psi equals approximately 6,894.76 Pa. Standard atmospheric pressure is about 14.696 psi.
The atmosphere (atm) and torr (mmHg) appear in chemistry and laboratory contexts. One standard atmosphere equals exactly 101,325 Pa and 760 torr. The torr, originally defined as the pressure exerted by one millimetre of mercury, is used in vacuum systems and in blood pressure measurement, where it is called mmHg. A healthy blood pressure of 120/80 means 120 mmHg systolic and 80 mmHg diastolic.
Pressure can be measured relative to a vacuum (absolute pressure) or relative to atmospheric pressure (gauge pressure). Tyre pressure is gauge pressure: a tyre rated at 35 psi gauge actually contains air at 35 + 14.7 = 49.7 psi absolute. This distinction matters in gas law calculations. The ideal gas law (PV = nRT) requires absolute pressure in pascals, not gauge pressure.
Vacuum is expressed as negative gauge pressure or as an absolute value approaching zero. Laboratory vacuum pumps are often rated in torr or mbar absolute. A rough vacuum is 1-100 torr; a fine vacuum is 1 mtorr to 1 torr; ultra-high vacuum goes below 10⁻⁹ torr.
How many psi is 1 bar?
One bar equals approximately 14.5038 psi. Conversely, 1 psi equals approximately 0.0689476 bar. For quick mental arithmetic, 1 bar is close to 14.5 psi.
What is standard atmospheric pressure in different units?
One standard atmosphere (1 atm) equals 101,325 Pa, 1.01325 bar, 14.6959 psi, 760 mmHg (torr), and 1013.25 mbar. These figures are fixed reference values, not averages.
Why is blood pressure measured in mmHg and not pascals?
Blood pressure measurement was standardised using mercury sphygmomanometers, where pressure was read as the height of a mercury column. The mmHg unit became embedded in medical practice and clinical standards worldwide. Although digital sphygmomanometers no longer use mercury, the mmHg unit is retained for continuity with decades of reference data and clinical guidelines.