A fat quarter is a piece of fabric 18" x 21". The piece may be a bit longer, perhaps 18" x 22", depending on the width of the fabric on the bolt. Fat quarter bundles consist of a number of fat quarters cut from a variety of fabrics - usually from a single fabric line. The number of fat quarters in a bundle varies quite a bit but typically is in the range of 25 to 40 pieces. Please see the individual product details for more information.