A chicken egg is the egg laid by a hen, and a typical egg from a modern laying hen is about 6 centimeters (2.4 inches) long. At its widest point it is about 4.5 centimeters (1.8 inches) across. The average chicken egg weighs about 57 grams (2 ounces).

Size

Eggs are sold by weight, not by length. The U.S. Department of Agriculture sorts them into six weight classes by the minimum weight of a dozen, from 15 ounces for Peewee to 30 ounces for Jumbo. A dozen Large eggs must weigh at least 24 ounces, or about 57 grams (2 ounces) an egg.

Poultry scientists in the United States measured eggs from a commercial strain of White Leghorn, the most common breed of laying hen in the country. The eggs averaged 64 grams, 59.9 millimeters long and 44.7 millimeters wide, with shells 0.47 millimeters thick. Eggs from a strain bred without selection since 1950 were almost as long, at 59.3 millimeters, but narrower, at 42.4 millimeters. Decades of breeding have made eggs larger and rounder.

Size comparisons

An average egg weighs about as much as a tennis ball, which weighs 56.0–59.4 grams, and is a little shorter than a tennis ball's diameter of about 6.7 centimeters.
An average egg weighs as much as 13 or 14 Anna's hummingbirds, which are 10 centimeters (4 inches) long, the next size up in the explorer.
The shell is about as thick as five sheets of paper, each about 0.1 millimeters thick.
The largest hailstone on record by diameter weighed 0.88 kilograms, as much as about 15 average eggs.
About five eggs laid end to end would span a 12-inch (30-centimeter) ruler.

How a hen makes an egg

An egg starts as a yolk released from the hen's ovary. It then travels through the oviduct, a tube 63.5–68.6 centimeters (25–27 inches) long, where the rest of the egg is added around it. After a short stop in the funnel at its entrance, the yolk spends about 3 hours in the magnum, which adds most of the white. It then spends about an hour and a quarter in the isthmus, which adds two thin shell membranes.

The egg then spends about 21 hours in the uterus, where the shell forms. From the release of the yolk to laying usually takes slightly more than 24 hours. About half an hour after laying an egg, the hen releases the next yolk.

What is inside

By weight, an egg is about 31 percent yolk, 58 percent white and 11 percent shell. The dry shell is about 94 percent calcium carbonate, in tiny crystals of the mineral calcite. Tiny pores run through it, and an air pocket forms inside, usually at the larger end, as a newly laid egg cools.

Shell color is inherited, passed down from parent birds to their chicks, and so are egg size and shell thickness. White Leghorns lay white eggs, which American shoppers ask for more than brown eggs, and that is part of the reason they are raised so widely.

Sources

Egg-Grading Manual. U.S. Department of Agriculture, Agricultural Marketing Service, 2000.
Shell Characteristics of Eggs from Historic Strains of Single Comb White Leghorn Chickens and the Relationship of Egg Shape to Shell Strength. Anderson et al., International Journal of Poultry Science, 2004.
Rules of Tennis 2026. International Tennis Federation, 2026.
Anna's hummingbird. Animal Diversity Web, University of Michigan Museum of Zoology, 2001.
Just How Small Is "Nano"?. National Nanotechnology Initiative.
Official Documentation of the Verification of the Vivian, SD Record Setting Hailstone of 2010. NOAA National Climatic Data Center, 2010.

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