Monday, 1 September 2014

The Mathemagical World of Quilting - Part One

I know, I know. I used the M word. Before you roll your eyes and reach for the Facebook button, this isn't one of those boring high school maths lessons we all loved to hate. It's a boring quilting maths lesson instead.

You may not have noticed, but maths is a huge part of quilting. Knowing the basics will help you determine the quilt size, backing or binding requirements, how big a block needs to be and much, much more. You could, of course, just download an app to do it all for you, but where's the fun in that?

Today we will look at the absolute basics of quilting maths. We will not be go into anything too complex at this stage. I wouldn't want your head to explode from pure boredom this early in the week.

Let's start with the whole inches vs centimetres thing. Frustrating right? Here are some pointers to help you out:
Note: These are approximate measurements to help with quilting. They're not scientifically accurate to the nth decimal point.
  • 1 inch = 2.5 centimetres. E.g. If a quilt measures 40 inches wide, it is approximately 1 metre wide.
  • 1 yard = 36 inches. This means that 1 yard is around 90 centimetres. If a pattern says 1 yard, order 1 metre. Then your stash will always be growing. See...maths really can be useful.
  • It is easier to just work in inches as most patterns and quilting tools are designed for inches. You're more likely to achieve the intended look of the pattern with a lot less accuracy issues. This is just my opinion though and I won't tell anyone if you decide to be a rebel and convert to centimetres.
Now let's have a look at determining the size of your quilt top. This is necessary for figuring out how much backing and binding fabric you will need. The easiest way is just to sew it all together and then measure. This isn't always convenient, though, as your quilt may not have the patience to wait for you to order backing fabric before it gets finished.

We will use the quilt from the Beginner Quilt Along as an example. This quilt is 8 x 5'' squares wide. Logically, we would multiple 8 by 5 and have our width...but aren't we forgetting something? What about those perfect 1/4'' seams? They need to be taken out of the equation. In such a small quilt, it may not seem all that necessary, but, the larger the quilt gets, the more inaccurate your estimate will be.

Here's where a little terminology comes into play: Unfinished and Finished sizes.
  • Unfinished refers to the size of a piece before it is sewn (when you can see the raw edges)
  • Finished is the size after it is sewn (all the raw edges are neatly hidden away in seams)
Using our 8 x 5'' example, we have an unfinished size of 5'' per square. Once the 1/4'' seams have been sewn, the finished size is down to 4 1/2''.
Note: The edge squares have not been sewn and, as such, will actually have an unfinished size of 4 3/4'' each. Confusing, isn't it?

The total estimated width for this quilt top is:
Width = 4 3/4 x 4 1/2 x 4 1/2 x 4 1/2 x 4 1/2 x 4 1/2 x 4 1/2 x 4 3/4 = 36 1/2''

Now go and try this with the height of 10 x 5'' squares. Comment below if you have any issues or would like to know more.

Part Two of this series will discuss how to use your estimates to determine your backing and binding requirements. Stay tuned for more exciting mathemagical adventures later this week.


  1. One of the reasons I became so interested in quilting was all the maths and logic that went into it. I love that part of it! I do often have to remind myself that 2½ + 2½ = 4½ but that's part of the fun of it!

    1. I secretly love the maths too ; ) I think it's why I took to quilting when I had Pepper and was no longer working. I was finally using my brain in that way again.