An over-the-range microwave should have a height clearance of between 13 to 16 inches from the top of the cooking range, according to GE's minimum requirements for appliances. This recommended height conforms to a minimum 66-inch mounting height from the floor to ensure unhindered performance.
The recommended height of 66 inches is a distance that is measured from the floor to the upper surface of the microwave. The distance between the top of the cooking range and the microwave is assumed to end at the bottom portion of the microwave. Over-the-range microwaves should not be installed above any cooking range that can generate over 60,000 BTUs.