More than 95% of the eggs commonly purchased by consumers in grocery stores are the regular white kind that come from battery caged hens. It's also what you eat in any kind of processed food that contains eggs. So this post is focused on this large majority.
The Canadian Coalition for Farm Animals has a helpful PDF with information on different kinds of eggs available for purchase.
It also provides a table that shows the battery cage standards for those different types of eggs. These standards are voluntary, but let's assume the eggs in the store come from producers who maintain the standards.
The table probably doesn't mean very much to the average person. But here is a really easy way to see it viscerally.
Take a sheet of regular 8 1/2" x 11" paper. You probably have several in front of you as you're reading this.
Now measure it. Or you can take my word for it. The area of that piece of paper is 574 cm2.
No, it's not what you're thinking. That is not the floor space allocated to a battery hen.
Take your piece of paper and remove 20% of it. If you want to be precise, you can cut off 6.9cm.
What you are left with is how much space a battery hen has to move around in, all her life. The standard floor space allocated to a battery hen is 432cm2.
Oh, and if you buy the pricier omega 3 eggs: they also come from battery chickens.