"The term "double knitting" originates from Great Britain and refers to a weight of yarn commonly used there. In the United Sates, the weight of DK yarn falls between worsted and sport weight. DK yarn is thinner than worsted weight yarn, but thicker than sport weight yarn. Different countries have different names and weights for their yarns, and DK yarn is no exception. In fact, the words "yarn" and "wool" once referred to worsted weight yarn, which in the United States is the most commonly used yarn. According to the Craft Yarn Council of America, DK yarn averages a knit gauge range (4 inches, or 10 centimeters, in stockinette stitch) of 21 to 24 inches on U.S. needles 5 to 7 (3.75 to 4.5 millimeters). DK yarn also is in the same category as light worsted. A pattern that calls for a light worsted yarn also can use DK yarn. The substitution should have little effect on the piece's size, but always check your gauge to be sure."