How do you calculate binding yardage?

The short answer: measure the perimeter of your quilt, add about 10 inches for the corners and the join, divide by the usable width of your fabric to get the number of strips, then multiply that by your strip width to get the fabric you need.

Here is the whole calculation, step by step.

How do you find the perimeter?

The perimeter is the distance all the way around the quilt. Add the width and the length, then double it:

perimeter = 2 x (width + length)

For a 60 by 80 inch quilt, that is 2 x (60 + 80) = 2 x 140 = 280 inches.

Why add 10 inches?

Binding is not just the raw perimeter. You lose a little length at each of the four corners when you miter them, and you need some extra to join the two ends of the binding into a loop. Ten inches covers both with room to spare, so 280 becomes 290 inches of binding to cut.

How wide should the strips be?

The common default is a 2.5 inch strip folded in half lengthwise, which gives a double-fold binding. Double-fold means two layers of fabric wrap the edge, so it wears longer than single-fold, and 2.5 inches finishes at a comfortable width for most quilts. If you like a narrower edge, some quilters cut 2.25 inches instead.

Cutting strips across the width of fabric

Strips are cut selvage to selvage, across the width of the fabric. Quilting cotton is about 42 inches wide, and closer to 40 usable inches once you trim the selvages. So each strip gives you about 40 inches of binding.

Take the total binding length and divide by that usable width, then round up, because you cannot buy part of a strip:

strips = 290 / 40 = 7.25, which rounds up to 8 strips.

A worked example: the 60 by 80 quilt

Putting it together for the 60 by 80 inch quilt with 2.5 inch strips:

Step	Value
Perimeter	2 x (60 + 80) = 280 in
Plus corners and join	280 + 10 = 290 in
Strips at 40 in usable	290 / 40 = 8 strips
Fabric	8 x 2.5 = 20 in
Rounded yardage	about 5/8 yd

So a lap quilt this size needs roughly 5/8 of a yard for a 2.5 inch double-fold binding.

What about other quilt sizes?

The math is the same for any size. Here are a few common ones with 2.5 inch strips and 40 usable inches:

Quilt	Perimeter	Total	Strips	Yardage
40 x 50	180 in	190 in	5	about 3/8 yd
60 x 80	280 in	290 in	8	about 5/8 yd
90 x 90	360 in	370 in	10	about 3/4 yd

When should you use bias binding?

Everything above is straight-grain binding, cut across the width of fabric. It is the right choice for quilts with straight edges and square corners, which is most quilts. If your quilt has curved or scalloped edges, cut the binding on the bias instead. Bias strips run at 45 degrees to the grain, so they stretch and ease around a curve without puckering. Bias uses a bit more fabric because of the angled cuts, so plan for extra if your edges are not straight.

Let the app do it

The quilt binding calculator runs this whole calculation the moment you type in your quilt size and pick a strip width. Sashing on iPhone does the same thing offline, so you can check your binding yardage at the cutting table without hunting for reception. Get the app and stop redoing the arithmetic every quilt.