The standard height for the distance between base cabinets and wall cabinets is 18 inches. While some cabinets may be slightly less, coming in at around 16 inches, and others may be slightly more, such as 22-inch cabinets, the standard height for all backsplashes is set at 18 inches. This is the distance from the top of the unfinished cabinet to the bottom of the wall cabinet, not from the top of the countertop to the bottom of the wall cabinet.
Custom cabinets allow you to disregard the standard measurements for backsplash height. While you can choose to use the standard 18-inch height, the beauty of cabinets is that the established guidelines are nothing more than a recommendation. You can build your cabinets in any way you see fit, hanging your wall cabinets at any height above the countertop to accommodate your custom cabinet plans. Most people use the 18-inch measurement because of the average human height, but you can adjust it as necessary.
A full backsplash, such as with tile or natural stone, runs from the top of the countertop on the base cabinets and up the wall to the underside of the wall cabinets. Any measurements you make for your backsplash should be made with the countertop material taken into consideration, as well as any light bars that may hang from the underside of the wall cabinets. Finish height is always different from the rough-in height, which is the established 18 inches.
The type of material you use on your backsplash can also dictate the height of your upper cabinets in relation to the base cabinets. For example, if you are choosing to run a large-bodied tile or natural stone slab, you may choose to adjust the height of the cabinets because it is easier to adjust those than cut certain types of materials. Or, you may want to run 4-inch tiles on a diagonal pattern and to avoid a small sliver cut on the bottom side of the wall cabinets, you could hang the cabinets higher to allow for a full-sized cut for visual appeal.