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Hydrostatic Pressure Explained
Hydrostatic pressure is what is exerted by a liquid when it is at rest. The height of a liquid column of uniform density is directly proportional to the hydrostatic pressure.
The formula for calculating the hydrostatic pressure of a column of liquid in SI units is: Hydrostatic Pressure (Pa, N/m2) = Height (m) x Density(kg/m3) x Gravity(m/s2) The density of a liquid will vary with changes in temperature so this is often quoted alongside hydrostatic pressure units e.g. inH2O @ 4 deg C. The local gravity depends on latitudinal position and height above sea level. For convenience the most common standard for hydrostatic pressure is metres or inches of water at 4 deg C (39.2 degF) with a standard gravity of 9.80665 m/s2. The density of pure water at 4 deg C is very close to 1000 kg/m3 and therefore this has been adopted as the standard density of water. Another reason for the significance of choosing 4 deg C is that it is very close to the temperature that water reaches its maximum density. In summary hydrostatic pressure units are a very convenient method for relating pressure to a height of fluid but they are not absolute pressure units and it is not always clear what density/temperature has been assumed in their derivation, so be very cautious when using them for high precision level measurements. In fact some institutions are discouraging their use because of the very reasons mentioned above. Pressure Measurement Resource Links Convert an altitude in feet or meters to a pressure unit Convert temperature units to and from degrees celsius, fahrenheit or kelvin Explain an IP rating for ingress protection Explanations for pressure measurement terms Create a pressure sensor specification in minutes for free
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Site Last Updated: 12/05/08
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