Please implement - the algorithm for changes in the size of the texture is not clear

Please implement - the algorithm for changes in the size of the texture is not clear. I reduce the value of X or Y, and the texture increases. And vice versa. Changing the size of the texture - in what units of measurement are set? Maybe it is worth introducing the size of the length and width of the texture in mm, cm or m? Then I can definitely introduce the dimensions of finishing materials and structures.