Originally Posted by kenn0223

The upstairs ones certainly are not. I don't think the mid-cabin ones in business or first are either. I vaguely recall the very aft ones in economy being slightly larger due to their shape, but not materially.

The only place I've noticed a much larger lav is the one behind 3AB on the 787 which is specifically designed as an accessible lav.

According to United.com's Accessibility Page, the 777 and 767 supposedly have wheelchair accessible lavs (which presumably are bigger to accommodate the wheelchair) but I haven't noticed them.

The Aircraft Page on United.com gives a pretty good depiction of the size of each lav on each aircraft (and does indeed show the larger one on the 787)