It's mid-Spring now in most parts of the country, and last year's chicks are really getting into the swing of laying eggs! (This year's chicks are still being raised, and will start laying around July or August.) A common question I hear this time of year is, why are my chicken's eggs so small?
The first thing is to distinguish between "regular eggs that are just a bit on the small side compared to supermarket eggs," and "this bizarrely tiny egg without a yolk, about the size of a quarter." The later are politely called "wind eggs," or more colorfully known as "fart eggs."
(I have illustrated this post with a picture of three regular eggs and one fart egg. For illustration purposes, and also because it's pretty funny. When I cracked open the fart egg, inside it was just egg white that was cloudy. This is normal.)
Next, we have to determine what size your eggs really are. The USDA egg grading manual averages weights over a dozen. Per egg, the average minimum weight is:
Large: 56 grams
Extra Large: 63 grams
Jumbo: 70 grams
Be sure to actually WEIGH your eggs before you start to worry. Your eggs will probably be physically smaller than grocery store eggs. But because the egg shell of a backyard chicken's egg is so much thicker, it will weigh more proportionately for a smaller egg.
I recently had occasion to crack a regular grocery store egg. I was shocked at how much larger it was than my own chickens' eggs, even though technically they are the same weight. And then I was shocked at how thin the eggshell was! And the yolk just looked pale and sad.
The grocery store experience tends to skew our expectations. Eggs come in all different sizes, and the "average" egg is a Large (56-62 grams). Even though we think of Extra Large or Jumbo as a "regular" egg, these are actually pretty big eggs.
Assuming that your chickens are getting enough fresh water and feed, there are several factors involved in the size of your eggs:
The Hen's Age
A pullet or a young hen will start out by laying eggs on the small size. The eggs will get bigger as she gets older. As a rule of thumb, the older a hen gets, the fewer, larger eggs she will lay.
Some breeds just lay larger eggs than others. Even within a breed, the variation between hens can be significant. Larger hens tend to lay larger eggs. Leghorns are generally accepted as laying the largest eggs, which is why most commercial egg production hens are a Leghorn cross.
Protein is the biggest nutritional factor in egg size. You can try blending some feed meant for meat birds (like Purina's Flock Raiser, 20% protein) in with your layer ration, to increase the overall protein percentage. However, it seems that increasing protein only increases the size of eggs for the first few months the hen is laying.
Above all, remember that quality is better than quantity! Even if your chickens' eggs are a little small, they are still FAR better than those freakishly big eggs you can buy at the store.