Chicken breasts vary greatly in size. A medium-sized chicken breast is about 200g / 7oz. If you are dealing with enormous pieces of meat (which seems to be the only thing that the supermarkets in Australia sell), it is best to cut the breasts in half horizontally, giving you four thinner slices of meat. This means they will cook evenly - a thick, fridge-cold piece of meat will dry on the outside when it is cooked through to the middle.