Hamburger patties shrink because of how they're formed and the loss of fat content as it's cooked away. If you choose lean meat for your patties, shrinking will be minimal, but you may still notice your perfectly sized patties are not so perfectly sized when finally cooked through. There's a technique you can use when creating the patties that reduces the shrinkage.
Wash your hands with soap and water. Put your ground hamburger into a bowl and add any seasonings you wish to use. Mix the seasonings into the meat with your hands.
Grab just enough meat for each patty as you can fit into your hand. Squish it between your hands and form it into a round patty.
Place each patty on a tray to transport later to the stove or grill. Press your thumb in the centre of each patty to make a small indentation, the "Sydney Morning Herald" advises. This prevents the patty from shrinking in on itself as it cooks.
Cook the patties immediately. Refrigerate the patties if cooking will take place later. If this is the case, remove from the refrigerator 10 to 15 minutes before cooking to eliminate some of teh chill.
Avoid the temptation to press the patty with your spatula to keep it from shrinking. It will flatten this way, but it also won't be as juicy because you're squeezing out the juices.