Do you mean the bubils that form on top? Some can be quite small depending on the variety. What variety do you have?
The bulbs underground also stay small. The onion is mainly used as scallions. If you grow them out to harvest the bubils, the underground bulbs willgrow to be about an inch in diameter. These are good for stews, soups roasts, etc.

By now they should have grown the cute little bulbs on top, ours do every yr. I toss away hundred of the bulbs growing on top. If you want some, contact me....I will send a padded envelop of just the top bulbs. Or else they go in the garbage, we just find them too hot to eat.
Darlene