If you are using stock or semi custom cabinets, the standard bottom alignment height of the uppers is 54" above the floor. It's that height so that the tall elements in the room align correctly at the top with the wall cabinets. Everything lines up as a standardized system. And appliance manufacturers use those standard dimensions to create their appliances. (Or at least most do take that 18" clearance into account.) Then, if light rail is desired, it's applied, which can take the clearance down to 16". But the bottom of the cabinet is still 54" above the floor.

If you are doing custom, then you can obviously do anything you want that you find functional, the rest of the world be damned. As long as your appliances fit under the cabinets, and you don't care a fig about resale, you could do the uppers 12" from the counter.

Thanks live_wire_oak

That makes sense and yes these are stock cabs. But I am really struggling with how the fact the light rail takes it down to 15.125''. The light rail trim is 2.375'' in height. That's where the problem is stemming from.

Iam trying to better understand is 18'' because visually it looks better, or is it 18'' because functionally it allows you to fit coffee makers, mixers etc.

I've never installed trim under my cabinets - is that necessary? I guess I like a simpler look and my light bars are very thin so I don't need trim to hide them. I'd be isn't concerned about whether my mixer or any other countertop appliance would fit under my upper cabinets.

Your light rail trim at 2.375", is that stock or custom? It isn't necessary to be that large for under mount lighting. 1 inch is fine for LED strips. My cabinets have just an inch but it is part of the cabinet face frame construction. 19" inches from counter. That is my prep area next to the cook-top. My other run of upper cabinets on the sink wall is 24" from counter. Awfully important for serious cooks having an area open for bread baking and juicing, blending. I have no appliances out at all. Don't like the clutter. All appliances are stored in my pantry wall. Your concern is valid but you need to make some decisions based on your personal cooking style reflecting your needs. It may not be a big issue if another counter surface is not encumbered by such a small clearance. When you scroll through kitchen reveals you will often see very small clearances in areas outside the major cooking triangle needing access to sink, fridge, stove. Often involves more storage than counter function but does balance overall.

Remember Ikea kitchens are mostly tiny and efficient use of space. Starter homes for the most part (though they work just as well in bigger open homes sometimes.) Walking through Ikea kitchen set-ups i feel cramped as well. The percentage of baby carriages wandering through, it is clear they are designed for a younger crowd looking for affordable function.

At our vacation rental beach house (new house built 2 yrs ago), the cabinets are frameless with uppers installed 19.5" above the counter (55.5" above floor) with 1.5" light rail, which brings the finished height down to 18" above the counter at the front edge of the cabinet. They are UltraCraft, which are semi-custom, so having my one full height cabinet built at 97.5 instead of normal 96" was no problem and no extra charge.

At our primary residence (built in 77), cabinets are 18" above counter, no light rail (and no under cabinet lights). The Vitamix will not fit under the uppers with the container sitting on the motor base. Just misses by 1/4". Waaaaaah !! I hate leaving it out on the counter with the container sitting next to the motor. I also hate pulling it out from the cabinet.

As stated above, if you lower your counter height, you could have problems with appliances not fitting properly (dishwasher, range, etc).

As far as the backsplash goes, I think it would visually close the space. Is there a reason you are going with a 4" backsplash ?