How to Calculate Quilt Block Sizes

Unless you are using a quilting pattern supplied to you from an outside source, you will need to know how to calculate the size of a completed quilt block. Furthermore, by understanding this process, you can plan quilt blocks of your own design to be a certain size by using the same calculation principles in reverse. This process calculates the size of a completed quilt block. It assumes that you are using a 1/4-inch seam allowance, which is most common in quilting.

Things You'll Need

  • Quilt block pieces

  • Seam gauge (ruler)

  • Paper

  • Pencil

  • Calculator

Step 1

Lay out the quilt block pieces as they will fit together when completed. Make sure all the edges touch but don't overlap.

Step 2

Measure the width of the entire loose block. Record this number as your raw width.

Step 3

Count the number of quilt pieces used in the width and figure ½ inch for each piece. This is the total seam allowance on both the right and left sides of the quilt piece. Record this number as your width seam allowance.

Step 4

Subtract the width seam allowance from the raw width. This new number is the completed width for your quilt block.

Step 5

Repeat this process for the height.

References & Resources