I think they're roughly the same size (if you take the whole conurbation), but surely smaller than Manchester/Birmingham which are second/third biggest.
I remember I was looking at Sheffield Uni back in the day and when I went up to see the place, they spent the whole day going on about how...
Rumour has it that if Wednesday and Leeds spend too many seasons in the same divisions, the combined gravitational effects of their bigness will create a supermassive black hole that engulfs the universe.