The width of fabric used is an important consideration when calculating the yardage used for a quilt backing. The C&T standard is to assume a 40″ width of fabric (WOF) which conservatively describes quilting fabrics. You may use a different number as long as it matches the fabric actually used in the project. Add from 4″ – 8″ to the width and length of the finished size of the quilt to determine the needed size of the quilt backing. This allows for shrinkage during the quilting process. An extra 4″ is added for small-sized quilts, while an extra 8″ is included for larger size quilts. Also, we add an extra 1/8-1/4 yard to the yardage calculation to allow for crooked cuts off the bolt.
The calculations follow.
For small size quilts with no piecing required:
If the backing cut length is 40″ (WOF) or smaller, then
yardage needed = [backing cut width + 4 1/2"] / 36″
If the backing cut width is 40″ (WOF) or smaller, then
yardage needed = [backing cut length + 4 1/2"] / 36″
For large size quilts requiring a pieced backing:
Using horizontal pieced seams
Backing cut length / 40″ (WOF) = # of pieces needed (round up to the nearest whole number)
yardage needed = [(# of pieces needed x backing cut width) + 9"] / 36″
Using vertical pieced seams
Backing cut width / 40″ (WOF) = # of pieces needed (round up to the nearest whole number)
yardage needed = [(# of pieces needed x backing cut length) + 9"] / 36″
For larger size quilts, you may want to calculate yardage using both vertical and horizontal seaming methods and buy the smaller calculated amount of fabric. Remember to cut off the selvages before piecing the backing.