You can get this from construction or hardware stores.
Tile over basement wall.
Place a second uncut tile over top of the open space overlapping the tile you just placed below make sure it is flush with the wall then use the bottom to mark the tile beneath.
Measure the distance from the edge of the wall to the edge of the last full sized tile installed on the row.
For tiling over tiles in bathroom walls you ll need to set up sheets of waterproof membrane in between the concrete wall and tiles.
Tile is available in many different sizes and styles and the price range is equally broad.
Be sure you double check the fit with the paper backing still on.
Subtract 1 4 inch from that measurement to get the necessary tile size.