Quilt binding formulas for every shape and size

Before we excitedly dive into a passionate mathematical discussion on quilt binding formulas, let’s joyfully reminisce about our schooling years for a moment…

Even as a self-confessed school lover/devotee/obsessive (What can I say?? My family rarely went on holidays!), never in a million years did I think that I would ACTUALLY use mathematical formulas (let alone QUILT BINDING formulas!) in my every day life.   I mean, c’mon, be honest now – how many of Present-You can honestly say that Past-You didn’t sit in a maths lesson and occasionally think, “WHY AM I EVEN HERE?  When am I EVER going to need to figure out the circumference of a circle while knowing only the diameter measurement, when I am a world-renowned hedge-fund manager/astronaut/opera singer*???  *hmmmph*”

*Ahem. Yes, I did actually want to be an opera singer. *sigh*  What talent the world missed out on… But also never in a million years did I think as a kid that I’d be a stay-at-home-mum to four kids who writes sewing patterns in her spare time.  So there’s that.  And turns out, that I HAVE had to work out the circumference of a circle using the diameter, along with several other mathematical formulas that once seemed completely superfluous to every day life.  So there’s also that.

Before we excitedly dive into a passionate mathematical discussion on quilt binding formulas, let’s joyfully reminisce about our schooling years for a moment…

Even as a self-confessed school lover/devotee/obsessive (What can I say?? My family rarely went on holidays!), never in a million years did I think that I would ACTUALLY use mathematical formulas (let alone QUILT BINDING formulas!) in my every day life.   I mean, c’mon, be honest now – how many of Present-You can honestly say that Past-You didn’t sit in a maths lesson and occasionally think, “WHY AM I EVEN HERE?  When am I EVER going to need to figure out the circumference of a circle while knowing only the diameter measurement, when I am a world-renowned hedge-fund manager/astronaut/opera singer*???  *hmmmph*”

*Ahem. Yes, I did actually want to be an opera singer. *sigh*  What talent the world missed out on… But also never in a million years did I think as a kid that I’d be a stay-at-home-mum to four kids who writes sewing patterns in her spare time.  So there’s that.  And turns out, that I HAVE had to work out the circumference of a circle using the diameter, along with several other mathematical formulas that once seemed completely superfluous to every day life.  So there’s also that.

Quilt binding formulas = quilt math

As it turns out, quilt math IS a thing.  So all you rebel school kids who spend your maths lesson daydreaming about the quilts you could be making, maybe you should pay attention because you do actually need to know some basic algebra if you want to be a quilter!  Righto, my quilty rebels, let’s do this!

Exactly what mathematical equation do we use to figure out how much fabric to cut to make enough binding to bind a quilt?  Well, first of all we need to figure out the sum of the lengths of the edges of the quilt, because the binding is attached to the perimeter of the quilt.  And what do we know about the word ‘perimeter’?  It’s a mathematical term, and there are mathematical equations we can use to figure it out!  *and the crowd roars*

There are a few different equations we can use to determine the perimeter of an object, and, wait for it…. each equation suits a different type of quilt!!  Maths is amazing, amiright?????  *heads nod enthusiastically*  Yay for quilt binding formulas!  Let’s start with the basics.

quilt binding formulas

Square quilts

Just like the shape, square quilts have four sides of equal length (give or take, depending on how accurate a quilter you are).  To obtain the perimeter of a square, we multiply the length of one side (L) by four.  That is,

Perimeter = 4 x L

Eg.  The perimeter of a square quilt with a side length of 40 inches = 4 x 40 = 160 inches.

Traditional rectangle quilts

Technically, there are lots of different types of rectangles, but we’ll start with the one that first comes to mind for the average human – that is, the one with 2 pairs of sides that have different lengths. (If that’s not what comes to mind for you, then you are not an average human.  Take it how you will.)  Two sides are the width measurement (W), and the other two are the length measurement (L).  To obtain the perimeter of this type of rectangle, we simply add the length and the width and multiply by two.  That is,

Perimeter = 2 ( L + W )

Eg.  The perimeter of a rectangle quilt with a length of 40 inches and a width of 30 inches = 2 x ( 40 + 30 ) = 2 x 70 = 140 inches.

Quadrilateral quilts

Now this one is for all my modern improv quilters who like to make quilts that aren’t bound to traditional shapes!  A quadrilateral is a shape that has four straight sides.  This is the only qualification, meaning that the sides don’t have to be the same length.  To figure out the perimeter of a shape like this you simply add all the sides together.  That is,

Perimeter = a + b + c + d

  Eg.  The perimeter of a modern quilt that has four unequal sides, measuring 43, 29, 21 and 33 inches = 43 + 29 + 21 + 33 = 126 inches.

But what about quilt binding formulas for more than four sides?

I thought you’d never ask!  Turns out I like to design quilts that are a little out of the ordinary (Exhibit A: the Flag version of my Strudel quilt).  So to determine the perimeter of the Strudel quilt we use the same equation as above, except we keep adding letters to match the number of sides of the quilt.  For the Strudel quilt, which has five sides, that would make the equation,

Perimeter = a + b + c + d + e

Eg. The perimeter of the twin sized Strudel quilt that has one side that measures 65 inches, two sides that measure 86 inches, and two sides that measure 38 inches = 65 + 86 + 86 + 38 + 38 = 313 inches. And this same equation can be used for any number of sides and sizes!  We’re living in such a topsy-turvy world these days that quilts can be any shape you want! 😉

Circle quilts

In the case of circles, the perimeter is called the circumference.  Depending on what measurement you have you can work out the circumference of a circle two ways.  If you know the diameter of the circle (which is the measurement of the width of the circle, from side to side and passing through the centre) the equation is,

Circumference = πD where π (or Pi) equals 3.14

Eg. The circumference of a circle quilt with a diameter of 30 inches = 3.14 x 30 = 94.2 inches. If you have the radius of the circle (which is the length of a straight line from the centre of the circle to the edge), the equation is,

Circumference = 2πr where π (or Pi) equals 3.14

Eg. The circumference of a circle quilt with a radius of 15 inches = 2 x π x 15 = 2 x 3.14 x 15 = 94.2 inches  

quilt binding formulas infographic

Quilt Binding Calculations

 

Minimum required binding length

Once you’ve figured out the perimeter or circumference of our quilt you can figure out the length of binding needed.  To make sure you have enough binding you need to take into account any corners in the quilt, joins in the binding and how much we need to make the final join in the binding when we attach it to the quilt.  My personal preference is to add about 15 inches extra to my quilt’s perimeter or circumference, which is a simple equation,

Binding length = Perimeter or Circumference + 15 inches

Eg. The minimum length of binding needed for the twin sized Strudel quilt = 313 inches + 15 inches = 328 inches

 

How much fabric do I need?

The amount of fabric you need to cut the required amount of binding is just another simple maths equation that requires three measurements to calculate –  the minimum length of binding (MLB) required, the width of the fabric (WOF) you will be cutting your binding from and the width of the binding you are making.  The equation is,

Amount of fabric required = (MLB / WOF) x WOB

Eg. Going back to my twin sized Strudel quilt, the amount of fabric required for the binding = ( 328 inches / 42 inches) x 2.25 = (7.8, rounded up to 8) x 2.25 = 18 inches Working backwards you can see that 8 strips of fabric that are 42 inches long will give us a total length of 336 inches, which should be enough to bind the quilt, when taking into consideration joins and corners. So that, my friends, is quilt binding calcs for quilts of all shapes and sizes!  And because we all love something to pin to a Pinterest board (check mine out here), here’s a Quilt Binding Calculations Cheat Sheet!

 

Now, tell me how to work out the circumference of an oval quilt

Ok, smarty pants, you’re on your own.

But seriously folks… have I covered everything in regards to quilt binding formulas?  Let me know if I’ve forgotten something in the comments!