Quilt math · Calculator
How to resize a quilt block
Make any block bigger or smaller and get every cut right, and know which sizes cut with a ruler and which need templates.
The short answer
Divide the new size by the block’s grid, then add the seams again; never scale the cut sizes. A 12″ Ohio Star’s 4½″ squares become 3½″ at 9″ and 2½″ at 6″, not 2¼″.
Work out yours
Free · no accountOhio Star at 9″ finished, 9½″ before it’s sewn in
Every piece cuts with a ruler
Background
- B2 squares 4¼″cut twice on the diagonals
- A4 squares 3½″
Dark
- B2 squares 4¼″cut twice on the diagonals
Accent
- A1 square 3½″
In Quarter Inch, change a quilt’s block size and every cut, yardage and template changes with it. It warns you when a size falls off the ruler.
Start designing freeThe app’s own cutting chart for the block alone: @quarterinch/cutting cuttingPlan · offRulerAt and rulerSizes
One block at 12″, 9″, 6″
The Ohio Star is a 3 × 3 grid: its squares and hourglass units are a third of the block. Here is Quarter Inch’s cutting chart for one block at each size. Notice that the cut sizes don’t shrink in proportion: the seam allowance stays ¼″.
| Piece | 12″ | 9″ | 6″ | Then |
|---|---|---|---|---|
| Background B: 2 squares | 5¼″ | 4¼″ | 3¼″ | cut twice on the diagonals |
| Background A: 4 squares | 4½″ | 3½″ | 2½″ | |
| Dark B: 2 squares | 5¼″ | 4¼″ | 3¼″ | cut twice on the diagonals |
| Accent A: 1 square | 4½″ | 3½″ | 2½″ |
Sawtooth Star
| Piece | 12″ | 9″ | 6″ | Then |
|---|---|---|---|---|
| Background A: 1 square | 7¼″ | 5¾″ | 4¼″ | cut twice on the diagonals |
| Background B: 4 squares | 3½″ | 2¾″ | 2″ | |
| Dark A: 4 squares | 3⅞″ | 3⅛″ | 2⅜″ | cut once on the diagonal |
| Accent C: 1 square | 6½″ | 5″ | 3½″ |
Churn Dash
| Piece | 12″ | 9″ | 6″ | Then |
|---|---|---|---|---|
| Background A: 2 squares | 4⅞″ | 3⅞″ | 2⅞″ | cut once on the diagonal |
| Background C: 1 square | 4½″ | 3½″ | 2½″ | |
| Background B: 4 rectangles | 4½″ × 2½″ | 3½″ × 2″ | 2½″ × 1½″ | |
| Dark A: 2 squares | 4⅞″ | 3⅞″ | 2⅞″ | cut once on the diagonal |
| Dark B: 4 rectangles | 4½″ × 2½″ | 3½″ × 2″ | 2½″ × 1½″ |
How to resize a block
- Find the block’s grid: how many equal squares it’s drawn on across. A Nine Patch or an Ohio Star is 3, a Sawtooth Star 4, a Log Cabin often 7.
- Divide the new finished size by the grid. That’s one grid square, finished.
- Work out each piece’s finished size from the grid squares it covers.
- Add the seams for its shape: ½″ for a square or rectangle, ⅞″ for a half-square triangle’s square, 1¼″ for a quarter-square triangle’s.
| The new block, finished | 9″ |
|---|---|
| One grid square: 9″ ÷ 3 | 3″ |
| A plain square: the grid square and ½″ | 3½″ |
| The hourglass units’ squares: the grid square and the quarter-square triangle’s seams | 4¼″ |
| The block before it’s sewn in | 9½″ |
Never scale the cut size. The 12″ block’s corner squares are cut 4½″. Scaled to half, that would be 2¼″. But the seams don’t halve: the 6″ block’s squares are 2″ finished, so they’re cut 2½″.
When a cut falls off the ruler
A rotary ruler is marked in ⅛″. When a new size divided by the grid isn’t a whole number of eighths, no line on the ruler gives the cut. Take a 10″ Ohio Star: its grid squares are 3⅓″, so you’d need templates for every piece. Quarter Inch spots this and says where it cuts cleanly instead: 9″ or 10½″.
A Log Cabin on a 7 grid is the classic case. At 12″ its logs are 1⁵⁄₇″ wide; it cuts cleanly at 10½″ or 14″.
| Block | Grid | 6″ | 8″ | 9″ | 10″ | 12″ | Cuts cleanly, 6″ to 14″ |
|---|---|---|---|---|---|---|---|
| Ohio Star | 3 × 3 | ruler | templates | ruler | templates | ruler | 6″, 7½″, 9″, 10½″, 12″, 13½″ |
| Sawtooth Star | 4 × 4 | ruler | ruler | ruler | ruler | ruler | every ½″ |
| Churn Dash | 6 × 6 | ruler | templates | ruler | templates | ruler | 6″, 7½″, 9″, 10½″, 12″, 13½″ |
| Snowball | 3 × 3 | ruler | templates | ruler | templates | ruler | 6″, 7½″, 9″, 10½″, 12″, 13½″ |
| Log Cabin | 7 × 7 | templates | templates | templates | templates | templates | 7″, 10½″, 14″ |
So choose a size the grid divides into whole eighths. For the Ohio Star, between 6″ and 14″, that’s 6″, 7½″, 9″, 10½″, 12″, 13½″.
What changes the answer
- Templates and paper piecing. Enlarge the finished shape, not the template with its seam allowance. Scale the drawing, then add ¼″ all around.
- Small pieces. Below about 1″ finished, pieces are fiddly to cut and sew. A 6″ Ohio Star has 2″ units; a Log Cabin at the same size has logs of ⁶⁄₇″.
- The triangles. Each shape has its own rule: see half-square triangles (finished and ⅞″) and quarter-square triangles (finished and 1¼″).
Questions
Short answers.
Something else? A real person replies.
hello@quarterinch.app
How do I make a 12″ quilt block into a 6″ block?
Halve every finished size, then add the seams for each shape again. A Ohio Star’s 4½″ squares become 2½″, not 2¼″.
Why doesn’t my resized block come out the right size?
Usually because the cut sizes were scaled, seam allowance and all. The seams are always ¼″: scale the finished sizes and add them back.
What sizes can I make a block?
Any size its grid divides into whole eighths of an inch. For a 3 × 3 block like the Ohio Star, from 6″ to 14″: 6″, 7½″, 9″, 10½″, 12″, 13½″. Other sizes need templates.
Can I resize a block on a photocopier?
For a drawing or a paper-piecing pattern, yes, but enlarge the finished lines only, then add ¼″ seams around each piece. Enlarging the seam allowance makes the block too big.