Other related units to it are the centimetre of mercury (cmHg), the foot of water (ftHg), the inch of water (inHg). Blood pressure is mostly measured by a sphygmomanometer, which is a mercury-based manometer. It is often used in aviation, medicine, meteorology, vacuum system, refrigeration. One millimetre of mercury is defined as the pressure exerted by one millimetre of a column of mercury at 0 ℃. It is a manometric unit based on mercury. The millimetre of mercury is a common unit of pressure. The relation between 1 atm and other units are as follows: Millimetre of Mercury (mmHg) The value of 1 atm approximately equals the atmospheric pressure at sea level. It is a standard reference pressure recommended by the National Institute of Standards and Technology (NIST). The standard atmosphere or one atmosphere (atm) is a standard pressure defined as 101 325 Pa. The bar is also an accepted unit in oceanography, engineering instead of the pascal. Figure 6: Pressures in the map is reported in mbar. Some scientists use the hectopascal hPa, the bar equivalent in SI, as a standard unit. The atmospheric pressures are reported mostly reported in mbar. Since then, the bar, precisely the minibar, remains a widely used unit in meteorology. He was a well-known meteorologist and contributed to modern weather forecasting. The bar was introduced by Norwegian scientist Vilhelm Friman Koren Bjerknes. The most common derived units of the bar are the millibar (mbar), the centibar (cbar), the decibar (dbar) and the kilobar (kbar). The bar is slightly less than an atomophere (1 bar ≈ 0.986 923 atm). Figure 5: Pressure Gauge Scaled in the bar It is a metric non-SI unit and defined exactly to 1 × 10 5 Pa. The bar is another common unit used to measure pressure. Note: one hectopascal is equivalent to one minibar. The hectopascal (hPa) is used by meteorologists to measure the pressure of air. The gigapascal (GPa) is preferred by geophysicists since the stresses and pressures within the Earth are in a large order of magnitude. The mechanical quantities like Young’s modulus, shear modulus, tensile strength, stiffness are displayed in the kilopascal (kPa) and the megapascal (MPa). The kilopascal is a widely used unit often atmospheric pressures are reported in kPa. The pascal is a very small unit, the micropascal is the smallest among them. The common derivatives of the pascal are the micropascal, the hectopascal, the kilopascal, the megapascal, and the gigapascal. The International Union of Pure and Applied Chemistry recommends 1 × 10 5 Pa as a reference standard pressure. The pascal can also be expressed in terms of the joule, which is the SI unit of energy. The pascal is the recognised SI derived unit of pressure and can also be expressed in terms of SI base units. Figure 4: One pascal is a force of one newton applied perpendicular to a surface of one square metre. One pascal is a force of one-newton perpendicular to a surface of one square metre. The unit pascal is christened after French mathematician Blaise Pascal. The SI unit of pressure is the pascal (Pa) or the newton per square metre (N m −2) or (kg m −1 s −2). Similarly for Pa to Torr, Conversion Scales mmHg to atm Figure 1: mmHg and atm Conversion Scale psi to bar Figure 2: psi and bar Conversion Scale psi to kPa Figure 3: psi and kPa Conversion Scale Pascal In the above equation, 1 Torr is the unit from the first column has a unit value, and the right-hand side of the equation, 133.322 Pa, is formed from the first-row unit and the conversion factor. A unit in the first column has a unit value (e.g., 1 Pa, 1 bar) while a unit in the first row have a value of its conversion factor. The first row and the first column represent the units and the remaining cells are the values. The above table is divided into units and values the values are conversion factors. Note: The above values are accurate up to six significant digits, and the values marked by † are exact values. Table 3: Pressure Units Conversion Table Units The conversion table below gives the relationship between some important units of pressure. Pound per square inch or pound-force per square inchĪn imperial unit of pressure, derived from psi Table 2: List of Nonstandard Units of Pressure Symbol The other nonstandard units of pressure are listed below.
It is a non-SI unit and a unit value of it is equivalent to 1 kilogram-force per square centimetreĪ non-SI metric unit, derived from the bar The table below list important units of pressure with its symbols.
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