Coefficient of Compressibility – Definition and Examples

Compressibility coefficient in compressible flow.
A compressible flow example(Image Source:

In fluid mechanics, the compressibilities of fluids are very important in the calculations. Because of this phenomenon, we call these fluids compressible or incompressible fluids. So, there is a coefficient that we can assess the properties of fluids. This is the coefficient of compressibility. Here you can find information about the coefficient of compressibility.

What is the Coefficient of Compressibility?

In general, we know that with increasing temperatures, the densities of fluids decrease and volume increases. And also, with the increasing pressures, the densities increase, and volume decreases. But these decrements and increments are changes with the type of fluids. So, the coefficient of compressibility is very important here.

For example, if we want to compress water by only 1 percent, we need to increase the atmospheric pressure to 210 atm. This is a very huge pressure change. So, we call the water incompressible fluid.

Also, if we want to compress the air by 1 percent by volume, we need to increase the pressure by only 0.01 atm. This is a very low-pressure increment. And again, we call the air compressible fluid.

So we have a coefficient which we call is as bulk modulus of elasticity or coefficient of compressibility. The unit of this coefficient is Pa or psi.

If the coefficient of compressibility increases, the required pressure to squeeze the substance increases. Also with the decreasing coefficient, this pressure requirement decreases.

Isothermal Compressibility

Isothermal compressibility is calculated with the inverse of the compressibility. The unis of it are 1/Pa or 1/psi. It shows the unit change of volume or density with the unit change of pressure.


So, you can use the compressibility coefficient to assess the compressibilities of fluids easily.

Finally, these are the general explanation of this coefficient.

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