Batting Size Calculator

Batting width is derived only from quilt top width plus overhang on both sides -- it has no dependency on quilt top length at all, since width and length are independent measurements of a rectangle. The same logic runs the other direction: batting length depends only on quilt top length and overhang, never on quilt top width.

3 to 6 inches per side is the typical range quilters use, and this calculator's default is 4 inches. More overhang gives extra margin against the quilt top shifting during quilting, especially with a longarm or hoop, but it also means more batting to trim and discard afterward once quilting is finished.

The calculator's Recommended Packaged Size will show "Custom (larger than King)", meaning none of the five standard pre-cut batting sizes it checks against (crib, twin, full, queen, king) are large enough. In that case you'll need batting sold by the yard off a roll rather than a pre-packaged batt, sized to your calculated Batting Width and Batting Length.

No -- the batting dimensions and area are calculated purely from quilt top size and overhang, with no shrinkage allowance built in. Cotton and cotton-blend battings commonly shrink 3-5% when washed or during heavy quilting, so if your project will be washed, consider adding extra overhang beyond the calculator's recommendation to compensate.