Standard sizes (L x W) are as follows:
King: 96" x 100"
Queen: 96" x 82"
Double: 90" x 76"
Twin: 90" x 60"
Crib: 65" x 50"
These dimensions allow the quilt to hang over the sides and bottom of the bed by about 12". If you prefer a quilt that lies on top of the bed with little overhang, look for quilts with smaller than standard dimensions.