How many triangles per square-in-a-square block?
Each block uses four side triangles and one center square.
Free quilting calculator
Square-in-a-Square Calculator
Square-in-a-square blocks are versatile and appear in many quilt designs. This calculator helps you determine the cut sizes for the center square and surrounding triangles.
Result
Square-in-a-Square cutting estimate
16 blocks at 12" with 6" centers.
- Finished block size
- 12"
- Finished center size
- 6"
- Side triangle cut size
- 8.99"
- Center square cut size
- 6.5"
- Total triangles
- 64
- Total center squares
- 16
- Triangle fabric yardage
- 4 yards
- Center fabric yardage
- 0.625 yards
Each square-in-a-square block uses four side triangles and one center square. The diagonal formula uses √2/2 ≈ 0.7071.
Formula
Side triangle cut size = (finished block size × 0.7071) + 0.5 inches. Center square cut size = finished center size + 0.5 inches.
Example calculation
For a 12 inch finished square-in-a-square block with a 6 inch center, cut triangles at about 8.99 inches and the center at 6.5 inches.
Results are planning estimates. Always round up when buying fabric, especially for directional prints, shrinkage, fussy cutting, or cutting mistakes.
Related calculators
Half-Square Triangle CalculatorCalculate HST cutting sizes and yardage for the two-at-a-time method or traditional method. Enter finished size and block count.Quilt Block CalculatorCalculate how many quilt blocks you need based on finished quilt size, block size, sashing, and borders.Fabric Yardage CalculatorEstimate fabric yardage from piece size, fabric width, quantity, seam allowance, and project type.
Frequently asked questions
What is the math behind square-in-a-square?
The side triangles are right triangles with legs equal to half the block size. The diagonal equals block size × √2/2.
Can I make oversized triangles for trimming?
Yes. Some quilters add 0.25-0.5 inches to the cut size and trim for accuracy.
What seam allowance is used?
A standard ¼ inch seam allowance is included in all cut sizes.