Eggs are available in sizes S to XL – extra large. This classification is defined by weight: a size S egg weighs less than 53g, size M goes up to 63g, L goes up to 73, and anything over that is XL.
The age and breed of the chicken determine the size of the egg
Egg size depends on two factors: age and breed of chicken. S-size eggs are almost always from pullets. And the older a chicken gets, the bigger eggs it lays. There are also differences between different chicken breeds. Much like the color of the egg is a breed issue, the size is also breed dependent. Brown hens lay particularly large eggs, while dwarf hens, as the name suggests, tend to lay small eggs.
Chickens probably do not feel pain when laying eggs
Regarding the question of whether chickens feel pain when laying eggs and even greater pain with large eggs: It is fundamentally difficult to find out scientifically because pain is an internal sensation – and chickens can neither speak nor communicate pain through facial expressions. There is therefore little evidence that laying eggs hurts them. It can be said that since the size depends on age and breed, i.e. natural factors, there is no reason to assume a connection between egg size and pain.
If you want to consider animal welfare aspects when buying eggs, the size of the eggs is therefore irrelevant. You should rather pay attention to the husbandry, i.e. buy free-range or organic eggs.