Difference between Hydrostatic and Osmotic Pressure

Published on July 16, 2015

Pressure is force per unit area. Osmotic pressure is the pressure that is needed to stop the transfer of a fluid in a semi permeable membrane, while hydrostatic pressure is pressure applied on a point in a fluid. The application of these concepts is very crucial in fields such as biology, plant sciences, hydrostatics and many more. It is therefore important to understand them in order to excel in jobs or professions in these fields. This article discusses what they are and the differences between them.


Osmotic pressure demonstration
Osmotic pressure demonstration

Osmotic pressure is the pressure required to stop the movement of a fluid in a semi permeable membrane. The fluid moves because of the different levels of concentrations between the two solutions, a solute and a solvent. Osmotic pressure occurs when the two solutions are divided by a membrane that allows the solvent to pass through it while preventing the solute from doing so. The solvent moves from the side with low concentration to the side with high concentration. Osmotic pressure is that force that can prevent this movement. In a way, osmotic pressure is referring to a gradient rather than an actual force.

Hydrostatic pressure demonstration
Hydrostatic pressure demonstration

Hydrostatic pressure is the pressure on any point on a fluid that is not moving. The pressure at that point is equivalent to the weight of the column of fluid directly above that point. This means that hydrostatic pressure is greatly influenced by the density of the fluid in which it is being measured, atmospheric pressure, acceleration due to gravity, and the level of fluid above the point of measurement.

Comparison Chart

Hydrostatic pressureOsmotic pressure
Can occur in a pure fluid or any fluid of the same concentrationOccurs in two fluids of different concentration
Does not involve a semi permeable membraneInvolves a semi permeable membrane separating the two fluids

Hydrostatic vs Osmotic pressure

What is the difference between hydrostatic pressure and osmotic pressure?

Both osmotic and hydrostatic pressure involve fluids. Osmotic pressure can only be present in special systems in which there are different concentrations of a fluid (solution and solvent) that are separated by a semi permeable membrane. Hydrostatic pressure can be present in any fluid that is static, i.e. not moving.

Osmotic pressure cannot be present in a solution with equal concentration. There have to be two solutions with unequal levels of concentration. Hydrostatic pressure can occur in a pure fluid or any fluid with any level of concentration.


For more information, watch this video to learn the difference on the example of blood system: