So, i'm working at a bathroom and my main problem is with tiles. My tile is 25cm x 75 cm how cand I apply exact measurement of my tiles to fit the walls. Let's sey I can hardly apply exact uv mapping on one wall, but is more hard to fit the other walls at the same measurement.
1: Create or resize a tile texture.
It should have the same proportions as the 75cm x 25cm tile, thats to say 75/25 = 3:1. To keep things simple I like the idea of having 1pixel to 1mm. In the example below the tile texture size is 750px x 250px.
3: Next is to UV unwrap the four walls A, B, C and D.
Before doing this it may make things easier if all all the surfaces that are not going to be tiled (UV unwrapped) are hidden (H key). Doing this will make it easier to select each of the remaining walls.
4: Hide wall A. Switch to the Back view (CTRL + 1), select Wall B and again UV unwrap using Project From View.
5: Unhide the Walls (Alt H)
6: Next we need to get the lower left corner of each wall island snapped to the lower left-hand corner of the UV space. This is done for two reasons, a) to have all the walls lower edges aligned and b) so that they can be all scaled up together from the same single point. (X=0 Y=0).
7: Uncheck the Constrain to Bounds.
Assign pivot point to 2D cursor and check that the 2D cursor is at X=0 Y=0. Select all four islands and scale them up until the right-hand edge of the Wall A is aligned with the right-hand edge of the UV space (X=1).
8: Now we are ready to do the final scaling. The length of Wall A divided by the length of the tile 6000mm/750mm = 8.
Another way to do this could be to use the Mapping node in the Node editor, adjusting the X and Y values to suit. In this case the UV Unwrapping (mapping) method would be Project from View (Bounds).
Because the length of Walls A and B are not the same as Walls C and D the scale of Y value would be different. This would mean having to use two different materials.