Quilt block grid calculator
Quilt block grid calculator: count the units across the block, then enter the finished size. On a 3×3 grid a 12″ block has 4″ units, and each starting square is cut at 4½″.
Any block, at any size
Nearest sizes that cut cleanly:
- Each unit finishes
- 4″
- So cut each unit
- 4½″
Scroll sideways to inspect every label.
Finished boundary 12″. 3 units across. One unit finishes 4″; cut it 4½″.
Why doubling the size does not double the cut
The rule is one line: divide the finished block size by the number of units across, then add ½″ of seam allowance to each plain square you cut. The allowance is fixed — it does not scale with the block — which is why doubling the finished size does not double the cut. The table below shows it at both sizes.
Scroll sideways to see every column.
| Units across | Unit at 6″ | Cut at 6″ | Unit at 12″ | Cut at 12″ | A block like this |
|---|---|---|---|---|---|
| 1×1clean sizes every ½″ | 6″ | 6½″ | 12″ | 12½″ | Square in a Square |
| 2×2clean sizes every 1″ | 3″ | 3½″ | 6″ | 6½″ | Broken Dishes |
| 3×3clean sizes every 1½″ | 2″ | 2½″ | 4″ | 4½″ | Card Trick |
| 4×4clean sizes every 2″ | 1½″ | 2″ | 3″ | 3½″ | Heart |
| 5×5clean sizes every 2½″ | 1.2″ | no cut — try 5″ or 7½″ | 2.4″ | no cut — try 10″ or 12½″ | Sister's Choice |
| 6×6clean sizes every 3″ | 1″ | 1½″ | 2″ | 2½″ | Churn Dash |
| 7×7clean sizes every 3½″ | 0.857…″ | no cut — try 3½″ or 7″ | 1.714…″ | no cut — try 10½″ or 14″ | Bear's Paw |
| 8×8clean sizes every 4″ | ¾″ | 1¼″ | 1½″ | 2″ | Log Cabin |
Column headings are the FINISHED size — what the block measures once it is sewn into the quilt. Every "cut" number is the size to cut one unit, which is the finished unit plus ½″ for the seam allowance on all four edges. The "clean sizes" notes are each grid's published steps; the calculator also accepts any in-between size the grid can genuinely cut, and refuses the rest. Where a row reads "no cut", that finished size cannot be cut accurately on that grid — the linked sizes beside it can.
Every block in this library, ready resized
Each of these has its own chart, computed at every size the block divides into cleanly.
- Bear's Paw
- Broken Dishes
- Card Trick
- Churn Dash
- Flying Geese
- Friendship Star
- Heart
- Jacob's Ladder
- Log Cabin
- Maple Leaf
- Nine Patch
- Ohio Star
- Pinwheel
- Rail Fence
- Sawtooth Star
- Shoofly
- Sister's Choice
- Square in a Square
Related pages
- Quilt block sizes Compare clean steps, cuttable eighths, and refused sizes.
- Finished vs unfinished block size Keep finished, sewn unfinished, and starting cuts distinct.
- Quilt blocks for beginners Start with the lowest computed scores.
Common questions
What size do I cut for a unit at 3 inches finished?
Cut 3½″ for a plain 3″ finished square — the finished size plus ½″. That rule covers any plain square or rectangle; triangle units are cut larger still, and each block page's chart carries those numbers ready worked.
Does this include seam allowance?
Yes. Every cut size this calculator gives already includes ½″ — the seam allowance on all four edges. Never add anything on top; adding it twice is one of the classic ways a block comes out too big.
What if my size isn't in the chart?
Type it into the calculator above — the table shows two sizes side by side to make a point, but the calculator takes any size. If your size lands on the ruler for your grid, you get the cut size; if it cannot, you get the two nearest sizes that can.
Why does the calculator refuse some sizes?
Because some sizes would put each unit between the marks on your ruler, and a cut you cannot measure is a cut you cannot repeat. Rather than silently round — and hand you a block that finishes wrong — it says no and offers the nearest sizes that work. The full logic is on quilt block sizes.