how loaf pan size affects bread

I have 3 loaf pans that all say they're 10x5 inches, but I think at least one of them is lying.  I believe my bread is a little dense because the pan I've been using lately has been something more like 8x4 inches.  My recipe is something like 450g flour, 72% hydration. 

Is there a general rule of thumb for how much dough goes in a rectangled loaf pan?  Is there a general ratio? Thanks!