How many panels fit on a piece of fabric.
Simple grid layout with no rotation; nesting odd shapes may fit more.
This calculator shows how many panels of a given size fit on a piece of fabric. It divides the fabric width by the panel width and the fabric length by the panel height, rounds each result down, and multiplies the two numbers. A 44 inch by 36 inch piece cut into 10 inch by 12 inch panels gives 4 across and 3 down, or 12 panels in all.
Try swapping the panel width and height to see whether turning the panels gives a better fit, if the fabric has no direction. Include the seam allowance in the panel size, since cut pieces need to be a little larger than the finished size.
Fabrics with a one way print, a nap, or stripes limit how you can turn the pieces, so you may get fewer panels than the calculation shows. Leave a margin at the edges for selvages, which are usually not used, and for any flaws.
Planning the layout on paper before you cut helps you see where scraps are wasted. Small leftover pieces can be saved for smaller projects, which makes better use of what you bought.