The size of a medium egg is 21 ounces. This is the weight of a dozen eggs. The same method is used for weighing other eggs in the US.
Egg Measurements Elsewhere
In Canada, the medium size is 49-55 g. The medium size in Europe is 53-63 g. In Western Australia, the medium size is 43 g. In the modern sizing scale used in New Zealand, the medium is 44 g.
How Eggs are Sized in America
The eggs are sized based on the collective mass of 12 eggs. The sizing is not based on the weight of an individual egg. The sizes are as follows: jumbo is 30 ounces; extra larger 27 ounces and large 24 ounces. This is followed by the medium size (21 ounces) and small at 18 ounces. The peewee is the smallest at 15 ounces.
How to Select the Right Size
Majority of recipes call for large size eggs. If you are just going to fry or cook simple recipes, the exact dimensions hardly matter. If the recipe calls specifically for medium or some other size, you can purchase them in grocery stores.
Eggs are graded according to quality. The highest quality eggs are labeled AA. This is followed by A and then B. The AA eggs are regularly shaped and are clear. The white are firm and the yolks are flawless. The air cell in grade AA eggs are 1/8 inches deep at most.
The A eggs are also of good quality, but the whites are not as firm. But the yolk is still well defined and without flaws. The size of a medium egg does not vary in the US. But they can be classified as AA, A or B depending on the grading.
Grading is necessary to determine their quality. This procedure can be performed by the state or federal officials. Majority of eggs sold are in the AA or A category. Some eggs sold have not been subjected to grading.
These ungraded eggs must at least reach the B standards. Eggs that do not meet this minimum standard are sold to factories that are capable of processing them. These eggs are not to be eaten.
The size of a medium egg is not something you will often use in cooking. But you can still get them if the recipe calls for it. Depending on the recipe, other types of eggs may be used.