Built-in microwaves typically have exterior dimensions designed to fit standard kitchen cabinet sizes, with many manufacturers producing ovens in widths of 19, 24, 27 and 30 inches. However, exterior dimensions do not always reflect the actual capacity of the oven itself.
Most built-in microwave ovens have widths between 19 and 24 inches, depths between 19 and 22 inches, and heights under 18 inches so the appliance can fit into kitchen cabinet spaces. Larger ovens usually have large capacities, but some are larger because of features such as convection cooking functionality. Capacities of built-in microwave ovens range between 1 and 2 cubic feet, with a typical capacity of 1.5 cubic feet.