Backsplash with uneven sides using decorative tiles

mcride244

I putting in a backsplash in the bathroom. It is 27 5/8 inches on the right side where the faucets will be, and 22 1/8 inches on the left side. It will be three rows altogether. I'm using a decorative tile in the middle row, and plain tiles on the first and third rows. The decorative tile is 3" x 12", but it has a 2 inch glass tile in the middle of the row which is placed in the middle of the tile in a diamond shape. How do I adjust the tile pieces so that the decorative tile will be evenly distributed? Thank you.