SQUARE IN A SQUARE

square-in-a-square calculator

One center square and four corner triangles. Calculate before cutting.

Your block dimensions

Unit

Which size are you starting with?

Finished block side（cm）

Seam allowance on every seam（cm）¼ inch = 0.635 cm; use the same seam allowance throughout.

Minimum trimming margin per outer edge（cm）Only enlarges corner pieces, not the center square.

Changing units converts current values. Calculations run in your browser; dimensions are not uploaded.

Cutting list

Center square × 1

15.4121 cm

Side shown to 4 decimals; not automatically rounded to a ruler grid.

Corner squares × 2

12.6 cm

Cut each diagonally once for 4 triangles. Rounded upward to 0.1 cm grid, including trimming allowance.

Finished block: 20 cm
Trim sewn block to: 21.27 cm (including seam allowances)
Theoretical minimum corner side: 12.168 cm
Actual trimming margin per edge: About 0.216 cm

Rounding the center changes the finished block size. If your ruler cannot cut that decimal, choose My existing center cut size, enter a practical cut size and recalculate the block.Why?

These geometric results have not been validated by sewing real fabric. Make one block to check seams and points before cutting a batch.

First distinguish three sizes

Finished size: The visible outer side after joining the block, excluding outer seam allowances.
Unfinished size: The sewn and squared block's outer side, including one seam allowance on each side.
Cut size: Fabric size before sewing. Cut one center and two corner squares, each split along one diagonal.

For the method using one center square plus four right isosceles triangles. Read the full guide and examples →