Thursday, March 22, 2012

Thursday Tidbit - Math For Quilters, Part 4

In this last installment of Math for Quilters, I'll show you how to figure out yardage for your quilt back and for binding.

BACKING:  There are many charts for calculating backing available in quilting resource books; however, I will give you my rule of thumb.

If the longest side of your quilt is 80" or less, you can piece your quilt back with a horizontal seam.
  • Add 6" to the width of your quilt top.
  • Multiply this number x 2 = Linear Inches Needed
  • Linear Inches Needed / 36" = Total Yardage Required
Cut the fabric in half cross-wise (selvedge to selvedge), remove the selvedges from the seam sides, then sew the two pieces together lengthwise (along the long edges).

If your quilt top is longer than 80", but no wider than 80", you can piece your quilt back with a vertical seam.
  • Add 6" to the length of your quilt top.
  • Multiply this number x 2 = Linear Inches Needed
  • Linear Inches Needed / 36" = Total Yardage Required
Cut the fabric in half cross-wise (selvedge to selvedge), remove the selvedges from the seam sides, then sew the two pieces together lengthwise (along the long edges).

If both the length and width of your quilt top is greater than 80", you will need to piece your back with 3 panels.

  • Add 6" to the width of your quilt top.
  • Multiply this number x 3 = Linear Inches Needed
  • Linear Inches Needed / 36" = Total Yardage Required
Cut the fabric in thirds cross-wise (selvedge to selvedge), remove the selvedges from the seam sides, then sew the three pieces together lengthwise (along the long edges).

BINDING:  The formula for calculating binding is a simple 4-step process, but you do need to decide how wide you wish to cut your binding before doing the math.  This is the calculation for cross-grain (WOF) binding.  If you want to make bias binding, I suggest you purchase 1 yard to minimize the number of seams required to piece your binding.

1.  (Length + Width of Quilt) x 2 = # Linear Inches of Binding Required
2.  # Linear Inches of Binding Required / 40" usable WOF = # Strips Needed
3.  # Strips Needed x Binding Width = # Linear Inches of Fabric Needed
4.  # Linear Inches of Fabric Needed / 36" per yard = Yardage Needed (rounded up)

For example, if I have a quilt that is 72" x 80", and I cut my binding 2-1/4" wide, here are the steps I would follow:
  • (72" + 80") x 2 = 304" of linear binding required
  • 304" / 40" = 7.6 strips needed (rounded up to 8)  If your calculation is very close to being a whole number before rounding up (like 5.8 or 6.9), I recommend adding one more strip to your count.  I'd rather have too much binding than not enough!
  • 8 strips x 2-1/4" wide = 18" of fabric needed
  • 18" of fabric needed / 36" per yard = 1/2 yard of fabric
I would then buy the next increment of yardage (5/8 yard) to allow for squaring up the fabric, etc.

I hope you have learned something from these last 4 posts.  I know it's a lot of information, but it's kind of like undergarments.  You need a good foundation for the the rest of it to look good!

Next week:  Buying a Sewing Machine!

1 comment:

Diane Murphy Vasil said...

Thanks so much for all of the Math information, I can't wait to actually use it for a project. Really looking forward to the sewing machine tutorial, definitely in the market in the next year.

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