18″ x 24″ rotary cutting mat. Omnigrid mats have several unique features that quilters appreciate. The mat reverses from a medium green with grid lines to a light grey without grid lines. The grey side is easier on eyes and is useful when working with different fabric values. Omnigrid markings are distinct and readable and they line up with Omnigrid rulers. The outer dimensions are 1″ larger than the grid lines, which gives a larger cutting area. The mat surface is smooth which keeps the rotary blade sharper longer.