Finished vs. Unfinished Sizes in Quilts
New quilters usually have questions about the terms used in quilt patterns, and two terms I'm often asked to explain are the finished size and unfinished size. Those two terms can be used to describe any component used when you make a quilt, but when written in patterns they most often refer to the finished size of a quilt block.
What Is a Quilt Block's Unfinished Size
A quilt block's unfinished size is its dimension after the block or other unit has been constructed but has not been sewn to another portion of the quilt.
The block becomes smaller when it's connected to something else because its outer seam allowance will be encased in the seam.
I usually include the unfinished sizes of individual components to help quilters check sewing and pressing accuracy as they work.
What Is a Quilt Block's Finished Size?
Finished size refers to a block or individual piece's dimensions after each of its sides is sewn to a neighboring component.
How Do the Sizes Differ?
We usually sew patchwork with a quarter-inch seam allowance. A seam of that size reduces the unfinished size by 1/2" vertically and 1/2" horizontally -- by 1/4" on each side that has been connected to something else.
How Terms Are Used in Quilt Patterns
You'll usually see notations that categorize a quilt block as a 12-inch, 10-inch, 9-inch or another size. When the word unfinished isn't used, the dimensions nearly always refer to the finished size of the quilt block -- finished is the size that's listed most often.
My quilt patterns usually list both finished and unfinished sizes, giving you the opportunity to check components as you work, and to help you make sure that patchwork's final dimensions are correct before you use the block in a quilt.
A Few Words About the Final Size of Blocks and Components
Before binding the quilt the quilt top still has a seam allowance running along its edges, so technically, the finished quilt size is not calculated by adding the finished dimensions of its horizontal and vertical blocks and other components.
Why does that happen? The outer seam allowances remain along the outer edges, even after they are covered in binding. The small difference isn't important unless a quilt must finish at a specific size.
In reality, the finished size of most quilts may be a bit smaller than the 'textbook' size. Quilts 'shrink' a bit during the quilting process, and it's very easy to accidentally make blocks and other components that are a bit smaller than they should be, too.
Don't worry about the differences if your blocks and quilts have matching seams, and if the points of triangles are not chopped off. If those things happen, you can improve piecing accuracy by perfecting a quarter-inch seam allowance and measuring and pressing as you work.
If quilt blocks are smaller than they should be, or if they are skewed, don't toss them aside. Use one of my squaring-up methods to get patchwork in shape for the quilt.