Cabinet Sizes
Most major cabinet manufacturers build cabinets using a standard of three-inch increments. They use this standard for simplification so that they won't have to manufacture cabinets of every inch combination in width and height. Each three-inch increment is a quarter of a foot representing four different cabinet size increments for manufacturing, as opposed to twelve. This is understandable considering there would be too many sizes involved to manufacture cabinets in one-inch increments.
Wall and base cabinet widths usually start at 9" and proceed as 12", 15", 18", 21", 24", 27", 30", 33", 36", 39" and 42". Though not every cabinet type is made in each of those sizes, for instance: sink cabinets are not offered in the smaller sizes, base corner cabinets such as Lazy Susan Cabinets or 90 Degree Corner Cabinets are generally 33" or 36" while Wall Cabinets of the same type are 24" or 27".
Wall and Tall Cabinet heights usually increase in 6" increments. Standard Wall Cabinets being 30", 36" and 42" and Standard Tall Cabinet heights of 84", 90" and 96". Wall Cabinet heights under 30" are typically in 3" increments with heights of: 9", 12", 15", 18", 21", 24", 27" but in limited widths.
Some companies offer cabinets that are taller, which are used for special purposes such as creating a China Hutch type piece of furniture, or for a situation in which a cabinet rests on the countertop and finishes at the same finish height as the other cabinets. An example is when an Appliance Garage is used. Many manufacturers make a cabinet that is an Appliance Garage on the bottom and a Corner Cabinet on top, but is one unit. Other manufacturers require the use of two cabinets to accomplish the same thing. One isn't necessarily better than the other though.