A large format tile is one that is 15" or longer on one side and can be as large as 40x120". Large format tile offers easier cleaning and maintenance but such large tile presents its own installation challenges. Larger tile is heavier so a stronger substrate is needed. An unlevel substrate can result in lippage. In a 10' installation only 1/8" of variation is allowable. The Tile Council of North America recommends a medium bed mortar and back buttering. Lastly, large format tile requires a 1/3" offset vs. the more common and traditional 1/2" offset to prevent lippage.