A medium sized cheeseburger without any mayonnaise will have an average of 340 calories. A large cheeseburger without any mayonnaise will have approximately 620 calories.
However, the amount of calories in a cheeseburger will vary depending upon the size of the burger, the brand of burger, whether the patty is small or large and whether or not it contains mayonnaise or not.
A Burger King Cheeseburger will have an average of 380 calories. A Whopper Burger King Cheeseburger with extra cheese will have approximately about 900 calories. A Wendy's Jr. Deluxe Cheeseburger will have approximately 420 calories.
A cheeseburger is nothing but a hamburger which contains a slice of cheese. It is fairly common for bigger cheeseburgers (like a cheeseburger made with two big hamburger patties) to have more than a single cheese slice. For variety grated or melted cheese is sometimes used in instead of, or in addition to, the grated or sliced cheese.