The thickness of an eggshell depends on the type of egg. The eggs that you most likely come into contact with are from chickens. Chicken eggshells are 0.35-0.37mm thick. (I tried to find this information in an old textbook about chickens, but gave up and just decided to measure it myself!).

Some variability may exist in eggshell thickness depending on the age of the chicken. Younger chickens produce smaller eggs, and these eggs may have thinner shells. However, this is unknown and would be an interesting science fair project. There is likely a minimum and maximum thicknesses of the eggshell as it must be thick enough to withstand being sat on by mom, but thin enough to allow oxygen exchange and the baby to break out! Larger bird eggs have thicker shells. Here is a picture of me measuring the thickness of an emu egg with an instrument called a caliper. The emu eggshell is over 3X as thick as the chick eggshell (1.05mm)! I wonder how thick a hummingbird eggshell is…

Eggshell thickness depends on many things, most importantly the animal. We most commonly see chicken eggs, which have a thickness of less than a millimeter. Ostrich shells, on the other hand, and significantly thicker and stronger, since they are also larger. They are a couple millimeters thick, like two pennies. Some eggs, especially in fish, have no real shell. This is because they are laid in water and do not need the same protection against dangers on land.

A chicken egg shell's thickness generally falls somewhere between 0.3mm and 0.7mm.