Preparing the backing for a quilt doesn't have to be a hassle or a pain.
To know how much backing you need, you will have to do a little math.
First, calculate the yardage needed to cover the width of your quilt plus 8 inches. If your quilt is 72 inches wide, that's 80 inches.
But, we also have to consider that most fabrics are 44/45 inches wide. So we need to order enough to cover the length. If your quilt it 90 inches long, you need at least 98 total inches to cover the back.
With horizontal seams - the best kind if you choose a pantograph or directional fabric- You will need 3 - 2 1/4 yard cuts, a total of 6 3/4 yards. If you request it cut this way at the store, it will be less work for you! You simply match the selvages, sew 1/2" before the selvage starts, until you have sewn the three pieces together and have two horizontal seams. Press these seams to one side and serge off the selvage or cut off the selvages in the seams. Leave the selvages on the ends. You will have quite a bit leftover after the quilt is quilted to use for another project! I'll be honest - I like the way horizontal backings look the best. 
A vertical seam may be less expensive, but it is more noticeable. Consider the above scenario where you need to back a 72x90" quilt. The 8 inches still apply - this is needed to load the quilt on the longarm. So you need to make a backing that is 80x98". You will need two lengths of fabric measuring 2.75 yards. This gives you enough length for the quilt. You sew them together by matching the selvages, sewing 1/2" inch away from the start of the selvage, and then cutting or serging the selvage off. The width of the fabric should equal around 88 inches. This only uses 5 1/2 yards of fabric and only has one seam.
If you want to make it easier on yourself - order a wide quilt backing fabric from us - no sewing required! Or order your backing fabric from us when you place your quilting order and we will sew it together for free!
Message us if we can help you calculate the amount of yardage you need!