Over-the-Range: These microwaves are designed to be installed above the range in the kitchen. They will typically have mounting brackets on the top and rear of the microwave chassis. Often times they will have fans on the bottom to help move the air beneath the microwave.
Compact: The smallest microwaves that sit on the counter are considered compact microwaves. For it to be considered compact, the microwave will have an internal capacity less than 0.9 cubic feet.
Mid-Size: The most common of all the microwaves on the market today. These middle sized microwaves have an internal capacity between 0.9 and 1.5 cubic feet.
Full-Size: The largest of all the microwaves sold today. To be considered a full-size microwave, the internal capacity will be greater that 1.5 cubic feet.