How big are they?

We have very large ones like Vidalias, small ones like pearl onions, and then everything in between. Most common are probably the size of an apple (how big is an apple, you ask?)

I searched for images on Google, I think this one matches the size of the onions I saw on the supermarkets near British Columbia University: https://www.khaleejtimes.com/uae/giant-red-onion-baby-head-s...

Serioulsy.

But as I searched , apparently they can get much bigger still! Search for "biggest onions" and you'll see.