Chicken egg sizes

Chicken eggs are graded by size, for the purpose of sales. The egg shell constitutes 8–9% of the weight of the egg (calculated from data in Table 2, F. H. Harms)
United States.
The United States Department of Agriculture sizing is based by weight per dozen. The most common U.S. size of chicken egg is 'Large' and is the egg size commonly referred to for recipes.
The following egg masses including shell have been calculated on the basis of the USDA sizing per dozen:
Canada.
In Canada, modern egg sizes are defined as follows:
Europe.
In Europe, modern egg sizes are defined as follows.
Post-Soviet countries.
In countries which are members of Interstate Council for Standardization, Metrology and Certification: Russia, Belarus, Moldova, Kazakhstan, Azerbaijan, Armenia, Kyrgyzstan, Uzbekistan, Tajikistan, Georgia, and Turkmenistan eggs are sorted into five categories by mass:
Australia.
In Australia, the Australian Egg Corporation defines the following sizes in its labeling guide.
In Western Australia, two additional sizes are also standardized by the Golden Eggs Corporation
New Zealand.
In New Zealand sizes are based on the minimum mass per egg:
Brazil.
In Brazil sizes are based on the mass. :
Animal welfare considerations.
According to Tom Vasey, chair of the British Free Range Producers' Association, laying larger eggs is painful for the hen. He recommends shoppers only to buy eggs of medium or smaller sizes. Professor Christine Nicol of the University of Bristol has stated 'There is no strong evidence of pain in egg-laying hens but it's not unreasonable to think there may be a mismatch in the size of birds and the eggs they produce. We do often spot bloodstains on large eggs.' 