Just measured one I have on a bed and it's 65" wide.

I did make this quilt with the thought in mind about how much it would hang on the sides of the mattress. Works perfectly.

OK. Thanks everyone! I appreciate your input.

I have always made my twin size quilts to measure 72 wide by 90 long.

Figure the top of the bed area and add drop for sides, and foot (if you need the foot). I found the quilts that are going on a bed that has a footboard are too cumbersome to get the quilt between the footboard and the mattress. Some like the sides to go down to the floor and others want to use a dust ruffle. Your choice. PS Don't forget to add the drop on both sides. Ask me how I know!!!!!!