Batting size and area for your quilt top, with overhang.
Long-arm quilters often want 4\u20138\u2033 of overhang on all sides.
Batting is the soft layer in the middle of a quilt, and it must be larger than the quilt top so the layers do not slip as you quilt. The batting size is the size of the top plus an overhang on each side, commonly two to four inches. A 60 by 80 inch top with a three inch overhang needs batting of at least 66 by 86 inches.
Batting is sold by the roll and in standard sizes such as crib, twin, double, queen, and king, so you may need to choose the next size up. The calculator also shows the area, which helps if you are buying batting by the yard.
Different kinds of batting behave differently. Cotton is soft and breathable, polyester is light and warm, and wool is warm and holds its shape. Check the package for how close together the quilting lines must be, and for any pre washing instructions.
Unroll the batting and let it relax for a day before you use it, so that the folds from the packaging relax. Trim any extra after quilting, and keep leftover batting for smaller projects such as place mats and table runners.