How eggs make the grade

• Photos

  This vintage Acme egg scale, for which a patent was granted on June 24, 1924, was the invention of Norton E. Chapman of St. Paul, Minn. It was once used to grade eggs according to their weight, as the scale's aluminum strips lifted according to the weight of the egg. The egg depicted here is a large. Photo by Sue Ade/Morris News Ser

This vintage Acme egg scale, for which a patent was granted on June 24, 1924, was the invention of Norton E. Chapman of St. Paul, Minn. It was once used to grade eggs according to their weight, as the scale's aluminum strips lifted according to the weight of the egg. The egg depicted here is a large.

Photo by Sue Ade/Morris News Ser

For the purposes of sales, chicken eggs are graded by weight. The United States Department of Agriculture grades them by minimum weight, per dozen, as follows:

Jumbo: 30 ounces

Extra large: 27 ounces

Large: 24 ounces

Medium: 21 ounces

Small: 18 ounces

Peewee: 15 ounces

Kitchen Ade note: The most common size eggs are large. When a printed recipe does not specify what size egg to use, it's generally assumed a large egg will be utilized.

When buying eggs, look for the U.S. Department of Agriculture grade shield on the carton with a grading of AA or A.