Surface tension is the property of a liquid which enables it to resist tensile stress. Surface tension is denoted by σ (sigma). Surface tension is expressed in N/m (Newton/meter). The force per unit length is the unit of surface tension.

When a liquid is contained in a vessel, it exerts force at all points on the sides and bottom of the vessel. The force per unit area is called intensity of pressure. Mathematically, intensity of pressure,
p = P/A
where
P = Force acting on the liquid, and
A = Area on which the force acts.

The intensity of pressure at any point, in a liquid at rest is equal to the product of weight density of the liquid (w) and the vertical height from the free surface of the liquid (h). Mathematically, intensity of pressure,
p = w. h

From this expression, we see that the intensity of pressure at any point, in a liquid, is directly proportional to depth of liquid from the surface.