[MAT] Absolute Scale of Texture

How do I force texture to have constant absolute scale in material? The goal is to have window hole (opacity mask cutout) with constant dimensions (like 1mx2m) in the middle of wall (plane), no matter what scale would the wall plane would be.No tilling at all, just one window.

So 5m x 8m wall would still have 1m x 2m window cutout in the middle.