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)
Lay out the quilt block pieces as they will fit together when completed. Make sure all the edges touch but don't overlap.
Measure the width of the entire loose block. Record this number as your raw width.
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.
Subtract the width seam allowance from the raw width. This new number is the completed width for your quilt block.
Repeat this process for the height.