Does anyone have a kitchen handy ?

What's the gap between the worktop and the underside of the wall units

The gap between the top of the base unit and the bottom of a 3 shelf high
wall unit should usually be 500mm. Subtract the worktop thickness from this
to get the measurement you are looking for.

This works for MFI and many other brands. However, you should allow any full
height or tall (to worktop) wall units to dictate the exact position. If you
have both full height and tall wall units, you may be limited to a specific
worktop thickness, usually about 40mm, or the tops won't align.

Christian.