A:Answer In the Atomic world of relative physics, an object of Exact size with that of an opening, will not allow for a suitable engineering fit. The opening must allow for the presence of air molecules for one surface to reside with another, where movement can occur.
However, I'm sure the manufacturers of this product, as well as the builders of the cabinets, engineered each of their creations to coincide in a standard of acceptance for installation.
True, your cabinets may be exactly 28.5", they are build to a very close tolerance. The manufacturers measurement of 28.5" or 28 1//2", are Not precise dimensions, and the measurement given is in reference to the standard cabinet to which they will very likely fit into, with an allowable tolerance for ease of installation, and with proper clearance.
The depth and most of the time, the height of the appliance is also standard to cabinet openings. Unless of course you have custom sized cabinets.
Given the width of the appliance and the width of your cabinets, I can safely assure you the width will be suitable. You yet have to confirm the depth and the height.
I've installed a number of these appliances, and still had to do minor adjustments, but they fit perfectly.
