Cake pan sizes are typically based on its shape and a measurement of the inside of the pan, going from one inside edge to the other. Round pans are essentially a measurement of the diameter of the circle made by the pan, and square varieties are simply measured from one side to the other. Rectangular pan measurements can include both sides, since they are different, and styles such as "bundt" and "loaf" often include the depth. The term "sheet " can also be used to refer to certain rectangular cake pan sizes, often as "quarter," "half," and "full."
One of the simplest ways in which cake pan sizes can be demonstrated or shown is through a direct measurement of them. For example, some pans might be described as 8 inch (about 20 centimeters) rounds or 9inch (almost 23 centimeters) rounds, indicating their size and shape. In this description, the measurement is taken across the middle of the round, from the inner edge of one side to the inner edge of the other. Similarly, a 10 inch (over 25 centimeters) square would describe cake pan sizes that are square in shape.
Other cake pan sizes indicate both the length and width of the pan, as well as the depth of it. This is common for types of pans that are fairly deep, such as loaf or bundt pans. The importance of depth for cake pan sizes stems from the speed with which heat from an oven is able to reach the middle of the batter. Baking in a loaf pan that is 4 inches (just over 10 centimeters) by 8 inches (about 20 centimeters) with a depth of 6 inches (over 15 centimeters) is going to be quite different from baking in one the same length and width, with a depth of only 3 inches (over 7 centimeters). The cake in the shallower pan will bake faster.
Cake pan sizes can also be measured in terms of "sheet" size, which refers to a specific type of shallow pan used for baking. A full sheet cake, and the pan used to bake it, is 18 inches (almost 46 centimeters) by 26 inches (about 66 centimeters) in size. This is commonly used in commercial baking, where a large cake of this size, consisting of two or three layers, can easily feed several dozen people.
A half-sheet pan is half this size, at 13 inches (about 33 centimeters) by 18 inches (over 45 centimeters). These are also quite common in bakeries, though they are small enough to fit into many home ovens. Cake pan sizes also include the quarter-sheet pan, which is about 9 inches (over 22 centimeters) by 13 inches (just over 33 centimeters).