A worked answer
A 50 by 65 inch throw has 230 inches of edge. Add 10 inches for joins, cut 2 1/2 inch strips from 42 inch fabric, and you are buying about 1/2 yard.
Perimeter is 230 inches. With 10 inches extra you need 240 inches of strip. Six widths of 42 inch fabric cover it. Six times 2 1/2 inches is 15 inches on the bolt, sold as 1/2 yard. The throw quilt designer is the 50 by 65 canvas; this page is only the edge.
Backing is how much backing for a throw quilt. Sewing is how to bind a quilt.
For a 50 by 65 inch quilt, cut 2 1/2 inch strips. The perimeter is 230 inches, plus 10 inches for joins. That is 6 strips from 42 inch fabric, which comes to 1/2 yard.
Usually not for 2 1/2 inch straight-grain strips on a 50 by 65 throw. Half a yard of full-width cloth is the shop cut this card uses.
Twin perimeter is longer. Use the twin binding page for 70 by 90.