Comforter sizes run slightly larger than mattress sizes to allow for draping over the sides of the bed. Typical sizes in the United States for comforters are: 1  Twin = 64 (163 cm) width × 87 (221 cm) length. 2  Queen / Full = 87 (221 cm) width × 87 (221 cm) length.  King = 101 (257 cm) width × 90 (229 cm) length.