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Why are there so many pressure units to convert to17th July 2008If you break down the SI unit (Systeme International d'Unites) for pressure which is the 'Pascal' (Pa) you can begin to understand why there are so many types of pressure measurement units. Since Pressure equals force divided by area, this introduces the SI measurement units for force and length which are Newtons and Metres. Force equals Mass multiplied by Acceleration, which adds the SI measuring units for mass, length and time which are Kilogrammes, Metres and Seconds. So we now have an SI unit for pressure which is derived from four fundamental units of measurement. Each of these SI units has many alternative units of measure. The Newton unit can be converted into short tonnes force, kilogram force, grammes force, long tons force, pounds force or ounces force. The Kilogram unit can be converted into metric tonnes, grams, milligrams, micro-grams, pounds or ounces. The Metre unit can be converted into centimetres, millimetres, feet or inches. The Second unit can be converted into minutes, or hours and so on. This is not an exhaustive list but already you could produce many combinations of units to create a unique pressure reading. If you now consider the applications for measuring pressure such as the weight that a hydraulic system must lift or the pressure of water at a certain depth or level, you will find that the most convenient pressure units to choose would be those that relate to the mass or the height of fluid. Although these units of measure are not constant with changing environmental conditions such as gravity and temperature there variation is small enough not to interfere with the required accuracy for the majority of pressure measurement applications. For the level of liquids it is mainly the hydrostatic pressure exerted due to the acceleration of gravity on pure water, sea-water and mercury that have been adopted for the pressure measurement units. For pressures derived from applied force it is the Bar unit (100,000 Pascals) or the PSI unit (6894.76 Pascal) that is most widely used. These units of measure provide the building blocks for most of the pressure units that are in common use today. Since measuring pressure is not a direct measurement like length or time it is more practical to choose units of measure that relate to their application rather than a unit that is less tangible, even if it is a sacrosanct SI unit. Which is easiest to relate to, 10 metres of water or 980,660.5 Pascals? Related Products Pressure gauges with selectable pressure units Associated Topics Differences between gauge and absolute pressure Vacuum measurement with absolute or negative gauge reference pressure Selecting the appropriate pressure reference Resources Pressure unit converter and conversion factors
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