By the hydrostatic pressure p inside a liquid at a certain point is meant the force F acted by the liquid perpendicularly on a test surface in the point divided by the area A of the test surface:

• The hydrostatic pressure is independent on the direction of the test surface.
• The hydrostatic pressure does not depend on the form of the vessel containing the fluid.
• The total force caused by the hydrostatic pressure on a horizontal area A is same as the weight of the liquid column, which has the bottom A and the height equal to the vertical distance h of A from the free surface of the liquid. This is the hydrostatic paradox. Thus,
  

  where ϱ is the density of the liquid and g the acceleration due to gravity.

The above laws have been discovered and experimentally proved by Simon Stevin (1548–1620).