Problem calculating the parapet height for a worktop running into the window

... It would be nice if we could get back to my actual question ...

Sure: forget it.

You simply cannot calculate exactly how inaccurately the masonry is done. You will have no choice but to determine the exact height of the parapet once the kitchen floor is fully tiled; and only then have the window installer measure concerning this window. Masons are, firstly, not precision mechanics, and secondly, they come before the screed and floor layers. So they could at most consider the planned build-up height of the floor in their mind if they work in the rough construction phase before that.

It is also possible that they only finalize the parapet height later: for example, you want 97 cm plus 18 cm floor, totaling 115; then they first build the four full rows of bricks (i.e., 100) and later see whether to cut the additional bricks to 15 cm height or do it differently.

But calculating everything so precisely that you could give all parties their exact work measurements before the foundation is laid: that would be the famous "counting your chickens before they hatch." And with a stroke through, the decimal places then don't matter.

The window installer will have to work a bit differently here because kitchen countertops are usually thicker than window sills; and you will hardly want to have this parapet height as a standard dimension for all your windows.

Then find out what your windows look like. Ours don’t have an extra profile underneath. They rest on consoles with the lower frame, and the countertop runs against it.

Hi,
we also have the kitchen countertop at 97 cm because we are both tall and that is a great height.
However, on the side of the house, we also have the same sill height at the 2nd window, which is the living room window, so it looks uniform from the outside.

Our kitchen planner spoke directly with our builder (although timber frame), and he then calculated the sill heights in combination with the windows we chose.
We did a lot ourselves, but I would always say to have these 3 people meet or discuss so that nothing goes wrong.

Best regards, Tina

However, on the house side we also have the same parapet height at the 2nd window, which is the living room window, so from the outside it looks uniform.

You get almost the same effect if you split the living room window in height, that is, by building a fixed "flower window" section below the opening sash.

Thank you very much for your answers. I can already tell that it is more complicated than I thought. Let's see how I can implement it. I will try to discuss it together with all parties involved.

Thank you very much for your answers. I already realize that it is more complicated than I thought. Let's see how I manage to implement it. I will try to discuss it together with everyone involved.

We calculated it like this: 10cm feet, 78cm kitchen carcass + 3cm thick countertop resulted in a height of 91cm. Our shell builder then set the parapet height at 104cm (104-17cm floor structure), which results in a finished height of 87cm. Now the countertop is placed on top of that (with a substructure) and we had our finished height of 91cm. The window fitter then measures the shell opening and makes a higher structure on the lower frame side so that later there will be an equally thick frame all around the window (about 5cm).
With your kitchen work height of 97cm, you have to keep in mind that most suppliers only offer carcasses up to 78cm height and then you get a 17cm high plinth, which does not look quite as nice if that matters to you.

Best regards
Sabine