What's the averave size for most dinosaurs?

I've read somewhere that giant size in dinosaurs is not the rule, but instead the exception.

Given there were over 700 species of dinosaurs with massive variation in size it is really meaningless (as well as impossible to calculate due to the poor fossil record for very many species) to talk about the average - it would be like asking what is the average size for all birds or reptiles.

Dinosaurs were, on average, at adult size pretty big (over a ton). It's a bit of a recent myth that they were mostly small.