Quilt math · Sizes and yardage
Finished vs unfinished size, and where the ¼″ goes
Patterns give two sizes for every block. Here’s what each means, where the ¼″ seam allowance goes, and how it changes what you cut.
The short answer
Finished is the size in the quilt; unfinished is before it’s sewn in, with a ¼″ seam allowance on every side. So an unfinished block is ½″ bigger: a 12″ finished block is 12½″ unfinished.
The difference
Finished is the size you see in the quilt, after it’s sewn to its neighbors. Unfinished is the size before that: the block or unit as it comes off your machine, with a ¼″ seam allowance still on every edge. The seam allowance is what gets sewn into the seams, so it never shows.
So a block is ½″ bigger unfinished than finished: ¼″ on each side. Patterns often give both: “12½″ unfinished (12″ finished)”. Measure your sewn block before you set it into the quilt: if it’s 12½″, you’re right on.
| Finished block | Unfinished (sewn, not yet set in) |
|---|---|
| 6″ | 6½″ |
| 8″ | 8½″ |
| 9″ | 9½″ |
| 10″ | 10½″ |
| 12″ | 12½″ |
| 14″ | 14½″ |
Where the ¼″ goes when you cut
Every piece is cut bigger than its finished size, so there’s fabric for the seams. How much bigger depends on the shape, because a seam along a diagonal takes more. For a 4″ finished piece:
| A square: ¼″ on each of four sides, ½″ more each way | 4½″ |
|---|---|
| Half-square triangles, two from a square cut once on the diagonal: ⅞″ more | 4⅞″ |
| Quarter-square triangles, four from a square cut twice: 1¼″ more | 5¼″ |
| A 4″ border: cut 4½″ wide | 4½″ |
The triangles are in half-square triangles and quarter-square triangles, with charts for every size.
A quilt’s finished size
The quilt’s outer edge has a ¼″ seam allowance too. The binding is sewn ¼″ in from the edge, so the quilt’s finished size is the size of the top, less ¼″ each side. A 4″ border cut 4½″ shows 4″: ¼″ goes into the seam with the quilt, and ¼″ into the binding.
Bed sizes in standard quilt sizes are finished sizes, and so is every size in Quarter Inch: the app adds the seam allowance when it works out the cuts.
Questions
Short answers.
Something else? A real person replies.
hello@quarterinch.app
What does unfinished block size mean?
The block’s size before it’s sewn into the quilt, with a ¼″ seam allowance still on every side: ½″ bigger than its finished size.
Is a 12½″ block 12″ finished?
Yes. Once it’s sewn to its neighbors with ¼″ seams, 12″ shows.
How much bigger do I cut a square?
½″ bigger than its finished size: 4½″ for a 4″ finished square.
Why is my block too small?
Usually the seam is a little wider than ¼″. Over several seams in a block it adds up. Test your seam with three strips, and press seams flat, not stretched.