There are many very mundane things you must take into account when deciding what size to make a bed quilt. Here's a step-by-step run-down of everything you need to know exactly how big to make quilted comforters and bedspreads. Sizing Your Quilt Top Start with the size of the bed's mattress. Fortunately, mattress sizes are fairly standard: Crib 23" by 46" Twin 39" by 75" Double 54" by 75" Queen 60" by 80" King 78" by 80" California King 72" by 84" Next, compute the "drop" -- the amount of quilt you'll need to hang over the edge of the mattress