How big is an egg ?

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I was at work the other day, where among other things we’re developing some eggcups, and the question came up and stuck in my head: How big is an egg?
We all know that you can buy eggs in various sizes, a bit like t-shirts: small, medium and large, depending on your needs for frying, scrambling or boiling.
But who decides how big an egg should be? Do chickens lay all their eggs the same size? Can one chicken lay both large and medium size eggs or are jumbo eggs only laid by jumbo chickens? Slightly intrigued by my dilemma I started researching.
Here in Europe you can buy four different sizes although I couldn’t find any small ones:

  • Small, weight must be less than 53grams
  • Medium, weight must be equal or larger than 53grams but less than 63 grams
  • Large, weight must be equal or larger than 63grams but less than 73 grams
  • Extra, large weight must be equal or larger than 73grams

I didn’t really find much information about diameter and height, which is what you are interested in if you intend making an eggcup, so I had to measure them myself.

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Another factor concerning the quality selection of eggs is the “grade”, those letters you find on the box like AA or A. These letters do not identify the nutritional quality of an egg or the freshness as one could initially believe. The letters rank the exterior and interior aesthetic of the egg, factors which influence a customer’s choice. Eggs are graded on cleanliness, shape, texture and soundness. B and C grade eggs also exist, these are the really ugly ones that don’t make it to the supermarkets and are instead used in processed foods and shampoos.

The size of an egg depends on many factors some regard the bird itself other regarding its environment and its nutrition. The breed, age and weight of a chicken are probably the most influential factors that determine egg size.
Hens will start laying eggs around 4 or 5 months of age, eggs will initially be small and sometime the shell will be soft and not properly developed, as months go by the eggs get bigger and stronger.

The coming and going of seasons naturally influence egg sizes, but in industrial egg farms all variables such as temperature, humidity and light are artificially controlled to maximise production and control size.

Apparently we know more about the nutritional requirements of the chicken than of any other domestic animal. Maybe in the olden days people would feed their chickens corn and a bit of grass, crushed oyster shells for added calcium, the kitchen scraps would usually end up in the pen too. But nowadays egg farms prepare their rations scientifically balancing amino acids and protein to ensure optimal cost effectiveness in breeding. It is also possible to quickly control the size of the eggs by altering the dietary balance of amino-acids.

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The food industry is well… an industry and industrial methods are applied to the growth, maintenance, packaging and transport of its product: our food. Eggs are certainly no exception from this process. Europe alone produces more than 10 million tonnes of eggs a year that’s about 113 billion eggs, which is equal to… I have no idea how many football fields, but it’s a lot of egg. To reach such high production rates industrial egg farms have adopted many controversial breeding methods such as battery cages, which have recently come under fire by national legislators in Europe and the US and are being banned in favour of cage-free systems where the animals are able to live a more natural and pleasant life. You can easily find disturbing material about battery cage breeding on youtube.

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Caged-hen eggs

Battery hens are kept in small cages, with each hen having less space than an A4 sheet of paper. Most farms have 4 or 5 birds per cage (20in x 20in) and cages are stacked six high. The hens are unable to perch, scratch or preen and their beaks are cut. They enter the cages as chicks and stay there until slaughtered about a year later.

Barn eggs

Hens are housed in single or multi-tier buildings. They have room to move, litter to bathe in and nest boxes to lay eggs. Hens are able to use perches, with at least 15cm per bird and no more than nine birds per square metre.

Free-range eggs

Similar to the barn system, allowing them to behave naturally and move freely. In addition, the chickens have outside access and no more than 1,000 birds can be kept per acre.

Organic free-range eggs

Usually kept in small units, in small flocks and spend more time outside. Under EU regulations, as many as 9,000 hens can be kept in one shed. But the Soil Association allows flock sizes of no more than 500 birds. All organic chickens must have access to grass. Their diet consists of organic cereals.

Most of my reference have been taken from: Commercial chicken meat and egg production. By Donald D. Bell,William Daniel Weaver,Mack O. North