If a recipe calls for large eggs, that’s not a guesstimate — it refers to a specific size designation of egg. Eggs are classified in a range of sizes, from “peewee” to “jumbo.” These size variations have to do with the chicken laying the egg. In general, the older the chicken, the larger the egg. Chickens can lay eggs from about 18 weeks old, albeit very infrequently. Peewee eggs come from extremely young chickens, whereas jumbo eggs (weighing 2.5 ounces or more) come from fully mature, healthy chickens in their prime.
Other factors that can impact the size of an egg are the weight of the chicken, its diet, and the conditions the chicken lives in. For example, hens exposed to more light before 19 weeks of age will start laying eggs earlier, meaning their eggs will be smaller. Large eggs (about 2 ounces per egg) are what most recipes call for, and large and extra-large eggs (2.25 ounces) are stocked most commonly at grocery stores.
Following size guidelines is important in baking because the size of the egg corresponds to an amount of liquid. A large egg contains about 3.25 tablespoons of liquid, and an extra-large egg is about 4 tablespoons of liquid, so a substitution of four extra-large eggs for four large eggs can drastically change a recipe.
