How deep are overhead kitchen cabinets?
Similarly, how deep should overhead cupboards be?
Standard below-bench kitchen cupboards are 600mm deep. Standard above-bench kitchen cupboards are 300mm deep. Use 900mm as a minimum kitchen benchtop height (I actually do 930mm now, as people are getting taller!) Your overhead cupboards will be between 600mm and 700mm above your benchtop.
Then, are all kitchen cabinets the same depth?
Most commonly, wall cabinets are 12 inches deep, since this provides a good compromise between storage space in the cabinets and workable countertop space below the cabinet. Above microwave ovens, a 15- to 18-inch deep cabinet is common, and above a refrigerator, a 24-inch deep cabinet is standard.
The reason for this is that 18 inches of clearance between base cabinets and uppers are regarded as the optimal working space, and with base cabinets generally 36 inches high (with countertop included) and 24 inches deep, upper cabinets beginning at 54 inches provides the desired 18-inch clearance.