Get a large jar lid (at least 1/2" deep) and put a piece of plastic wrap over it. Grab your handful of hamburger meat mixture and pack it into the lid (I have it over the top a little). Turn the lid upside down onto your hand and peel off the plastic wrap. ... VOILA! the same sized hamburger patties every time!
With 1 lb. of hamburger meat, plus 2 pieces of crumbled fresh bread (and herbs, seasonings), I got 4 perfect patties.
ANOTHER TIP: I spray each side of the hamburger patties with olive oil non-stick spray, so they won't stick to the BBQ grill.