The tile line
When a wall is tiled up to a height, the tile covers the walls up to that line and the paint the walls above it. A window that crosses the line is split: the part below comes off the tile, the part above off the paint.
In the example bathroom of 2 × 1,6 m and 2,4 m high, tiled to 2,1 m, that gives 13,35 m² of tile and 2,1 m² of paint.
Count a room

