Quilt Lessons: How to Resize Quilt Blocks

For many quilters, resizing quilt blocks is something to avoid. And if you’ve ever tried to resize a quilt block, you know there’s some math involved. Don’t let that scare you away!

Changing the size of quilt blocks is much easier than it looks. Plus, learning how to modify the size of your quilt blocks can open the door to new quilt design possibilities. Once you know the basics, you can adapt quilt patterns to the finished quilt size you desire.

Resizing quilt blocks just takes a few simple math formulas—no calculus involved!

The first step in modifying any quilt block is to decide on the size of your finished quilt block. You can come to a decision based on a number of factors: doubling a pattern, cutting your pattern in half, or choosing the size based on your available fabric.

NOTE: When working from a pattern’s cutting instructions, make sure you remove the seam allowance before doubling or tripling the size. For instance, if your pattern calls for 3-1/2″ squares, first you’ll subtract the sum of the seam allowances (1/2″), double the finished block size (from 3″ to 6″), and add the seam allowance back in (1/2″). So, when all is said and done, you will cut a 6-1/2″ piece of fabric.


Below are the formulas for modifying basic quilt blocks (taking seam allowances into account):

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Resizing Square Blocks:

Square blocks are the easiest to resize. Simply add to your finished block measurement. For example, if you’d like your finished block to be a 4″ square, you’ll need to cut a 4-1/2″ square of fabric.

Resizing Rectangular Blocks:

Similarly to the square, for rectangle blocks, you’ll add to the length and width measurements of your finished block. If you’re doubling block that measures 3″ x 4″ in your quilt, you’ll cut a 6-1/2″ x 8-1/2″ rectangle of fabric.

Half-Square Triangle Blocks:

When you want to change the size of a Half-Square Triangle block, add 7/8″ to the desired finished block size. To make a 4″ finished block, you’d cut 4-7/8″ squares.

Quarter Square Triangle:

Since there are two cut lines and two seam lines in a Quarter-Square Triangle block you’ll need to add 1-1/4″ to the desired finished block size. For a finished block that’s 4″, you’d cut your squares 5-1/4″.


Pin this article to your Pinterest quilting board (just click on the image above) or write down these measurements so you can refer to them while quilting. As with everything, after a little practice, resizing quilt blocks will become second nature—a technique you’ll utilize when the need arises.

For those of us who are visual learners, I’d recommend the FREE video series called My First Quilt with Sara Gallegos. Start with her Basic Quilt Math with Squares and Rectangles video and when you’re ready to try the triangle watch her Basic Quilt Math with Triangles video.

Happy quilting!

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