This tutorial is written to show how to think about piecing a back that works for the size quilt top you have finished. Each size is listed as “averages” because all quilts are different sizes. Don’t take these measurements as gospel, you will still need to measure.
Standard practice for quilting on a domestic machine is to add 2” to 4” to all four sides of your quilt top. This will give you the minimum size that your backing should measure.
Next, section piecing by matching measurements closest to 44” or the Width of Fabric (WOF) first. If you can sew two WOF sides together and get close to one side of the quilt start there. Then determine how many yards you need to cover the opposite measurement.
Average Measurements by Standard Quilt Size
Estimated Yardage for a Crib/Baby is 1 1/2 yards.
Estimated yardage for a Throw is 4 1/2 yards.
Estimated yardage for a Twin is 5 yards.
Estimated yardage for a Full/Double is 5 yards.
Estimated yardage for a King size is 7+ yards. 
