How many eggs do birds lay?

You need to be more specific as to the type of bird. Also, are you referring to eggs laid at once (in a "clutch") or over the lifespan of the bird?

The typical number of eggs that a bird will lay varies considerably from species to species. Though, for practical reasons, birds cannot lay more than about 20 eggs at once - whereas reptiles (the other main hard-shell egg-laying group) can lay multiple dozens of eggs at a time.