If we know the size of the force (F) and the area over which the force is applied (A), then we can calculate pressure using
P = \displaystyle {F \over A}
Here is the outline of a pupil’s shoe, it’s drawn on graph paper so that the area can be calculated quickly by counting the large squares. Each large square is 1 square centimetre – we counted the approximate area by considering only whole squares inside the black outline of the shoe.
Assuming a mass of 50kg, the pressure when wearing these flat-soled shoes is
P = \displaystyle {{(50 \times 9.8)N} \over {0.0306m^2}} = 16000Nm^{-2}
The red shaded area of our photo shows the reduction in area when heels are worn. With heeled shoes, the area is reduced to approximately 1 square cm per shoe. The change in the pressure is staggering:
P = \displaystyle {{(50 \times 9.8)N} \over {(0.0002)m^2}} = 2450000Nm^{-2}
The Science Babe has made a video on this topic.