Square in a Square quilt block
A square set on point inside four corner triangles. It is the simplest way to turn a single square forty-five degrees, and it underpins a surprising amount of quilt geometry.
Also known as Diamond in a Square, Economy Block base.
Square in a Square is ancient in quilting terms and central to Amish design, where a large Diamond in a Square became the signature medallion of Lancaster County quilts. Its usefulness is structural: it converts an on-point element into a straight-set block, which is how quilters put diamonds into grid quilts without cutting setting triangles.
Square in a Square cutting chart
Cut sizes include a ¼″ seam allowance: ½″ on squares and rectangles, ⅞″ on half-square triangles, and 1¼″ on quarter-square triangles. Pick a finished block size:
| Fabric | Shape | Cut size | Qty | Notes |
|---|---|---|---|---|
| Background | HST square | 3⅞" × 3⅞" | 2 | cut once on the diagonal → 4 triangles |
| Dark | HST square | 3⅞" × 3⅞" | 2 | cut once on the diagonal → 4 triangles |
| Fabric | Shape | Cut size | Qty | Notes |
|---|---|---|---|---|
| Background | HST square | 5⅜" × 5⅜" | 2 | cut once on the diagonal → 4 triangles |
| Dark | HST square | 5⅜" × 5⅜" | 2 | cut once on the diagonal → 4 triangles |
| Fabric | Shape | Cut size | Qty | Notes |
|---|---|---|---|---|
| Background | HST square | 5⅞" × 5⅞" | 2 | cut once on the diagonal → 4 triangles |
| Dark | HST square | 5⅞" × 5⅞" | 2 | cut once on the diagonal → 4 triangles |
| Fabric | Shape | Cut size | Qty | Notes |
|---|---|---|---|---|
| Background | HST square | 6⅞" × 6⅞" | 2 | cut once on the diagonal → 4 triangles |
| Dark | HST square | 6⅞" × 6⅞" | 2 | cut once on the diagonal → 4 triangles |
| Fabric | Shape | Cut size | Qty | Notes |
|---|---|---|---|---|
| Background | HST square | 8⅜" × 8⅜" | 2 | cut once on the diagonal → 4 triangles |
| Dark | HST square | 8⅜" × 8⅜" | 2 | cut once on the diagonal → 4 triangles |
How it goes together
A centre square with four triangles added to its sides. Add opposite pairs, press, then the remaining pair, and trim square with a quarter inch beyond the centre square's points.
Tips
- Leave a quarter inch of background beyond every point of the centre square when you trim, or the points will be cut off in the next seam.
- The corner triangles have bias on their long edge — handle them gently and press without dragging.
- Stack two of these at different scales and you have an Economy Block.
How much fabric for a Square in a Square quilt?
Yardage for a whole quilt of Square in a Square blocks, computed the way the studio does it — every piece packed across a 40″ usable width with 10% added for waste.
| Quilt size | Blocks | Finished | Top fabric | Backing | Binding |
|---|---|---|---|---|---|
| Baby 36×48 | 12 | 36" × 48" | Background 1⅛ yd · Dark 1⅛ yd | 2½ yd | ⅜ yd |
| Throw 60×72 | 30 | 60" × 72" | Background 2⅝ yd · Dark 2⅝ yd | 3⅞ yd | ½ yd |
| Queen 90×108 | 72 | 96" × 108" | Background 6⅛ yd · Dark 6⅛ yd | 8¾ yd | ⅞ yd |
What it looks like in a quilt
A single block only tells you half the story. Set sixteen of them together and the secondary pattern appears where the blocks touch:
Square in a Square questions
How big should the corner triangles be?
For a centre square that finishes at X inches, cut two squares at (X ÷ 1.414) + ⅞ inches and cut each once on the diagonal. FourPatch calculates this for whatever centre size you pick.