Quilt Square in a Square Calculator: Center and Corner Cut Sizes

Work out square in a square cut sizes before you cut. Enter finished block size and blocks needed, and see center square cut size, corner square cut size, squares needed and unfinished block size, with the formula in steps.

Calculate your square in a square cut sizes

Finished block size in

Blocks needed

Blocks needed is a whole number, greater than zero. Count blocks by fabric combination, not by quilt, if different blocks use different fabrics.

This calculator is for one square in a square block size at a time. It does not calculate block layout for a whole quilt top. For block layout, use the Block Size Calculator. For fabric yardage, use the Fabric Calculator.

This calculator uses the traditional center square on point method only, with one center square and two corner squares per block. Cut each corner square once corner to corner, to make 4 corner triangles per block. For half-square triangles, use the HST Calculator. For block layout, use the Block Size Calculator.

Your result

Enter your measurements, then calculate.

How the calculator works

Step 1: Center square cut size

Center square cut size equals finished block size divided by 1.414, plus 0.5 inch, rounded up to the nearest 1/8 inch. The number 1.414 is the square root of 2, which comes from the diagonal of a square, because the center square is set on point inside the block. For finished block size 6 inches, center square cut size equals 6 divided by 1.414, which is 4.24, plus 0.5, which is 4.74, rounded up to the nearest 1/8 inch, which is 4.75 inches.

Step 2: Corner square cut size

Corner square cut size equals finished block size divided by 2, plus 0.875 inch, rounded up to the nearest 1/8 inch. Cut 2 corner squares of this size per block, then cut each once corner to corner, to make 4 corner triangles. For finished block size 6 inches, corner square cut size equals 6 divided by 2, which is 3, plus 0.875, which is 3.875 inches, which is already a whole 1/8 inch step, so no rounding up is needed.

Step 3: Squares needed and unfinished block size

Each block needs 1 center square and 2 corner squares, which make 4 corner triangles. For blocks needed 10, center squares needed equals 10 times 1, which is 10 squares, and corner squares needed equals 10 times 2, which is 20 squares, which make 40 corner triangles. Unfinished block size equals finished block size plus 0.5 inch, because seam allowance 0.25 inch on each side is still on the block before it is sewn into a quilt. For finished block size 6 inches, unfinished block size equals 6.5 inches.

Assumptions, shown next to the result

This calculator uses the traditional center square on point method only, with seam allowance 0.25 inch on each side, as is standard for piecing. Cut sizes are rounded up to the nearest 1/8 inch, so cut sizes may be a little larger than the raw formula result, which gives a little room for trimming the block to unfinished size after sewing. Cut sizes are used as entered in the unit mode you choose, with no extra added for mistakes or shrinkage, beyond the rounding up already in the formulas. Corner triangles are cut on the diagonal, so their long edges are on the bias, and they need careful handling so they do not stretch.

Square in a square cut size chart

This chart uses the same formulas as the calculator: center square cut size equals finished block size divided by 1.414, plus 0.5 inch, rounded up to the nearest 1/8 inch, and corner square cut size equals finished block size divided by 2, plus 0.875 inch, rounded up to the nearest 1/8 inch.

Finished block size	Center square cut size	Corner square cut size
2 inches	2.00 inches	1.88 inches
3 inches	2.63 inches	2.38 inches
4 inches	3.38 inches	2.88 inches
5 inches	4.13 inches	3.38 inches
6 inches	4.75 inches	3.88 inches
7 inches	5.50 inches	4.38 inches
8 inches	6.25 inches	4.88 inches
12 inches	9.00 inches	6.88 inches

Chart values are a guide for the finished sizes shown. Your own finished size may give a different result. Use the calculator above for your own measurements.

Worked example, checked against the calculator

Finished block size 6 inches, blocks needed 10.

Center square cut size: 6 divided by 1.414 equals 4.24, plus 0.5 equals 4.74, rounded up to the nearest 1/8 inch, which is 4.75 inches.

Corner square cut size: 6 divided by 2 equals 3, plus 0.875 equals 3.875 inches. Cut 2 corner squares of this size per block, then cut each once corner to corner, to make 4 corner triangles per block.

Squares needed: center squares 10 times 1 equals 10 squares, corner squares 10 times 2 equals 20 squares, which make 40 corner triangles.

Unfinished block size: 6 plus 0.5 equals 6.5 inches, before the block is sewn into a quilt.

Frequently asked questions

How do I calculate square in a square cut sizes?

Center square cut size equals finished block size divided by 1.414, plus 0.5 inch, rounded up to the nearest 1/8 inch. Corner square cut size equals finished block size divided by 2, plus 0.875 inch, rounded up to the nearest 1/8 inch. For example, a 6 inch finished block needs a 4.75 inch center square and 3.875 inch corner squares.

What is a square in a square block?

A square in a square block sets one square on point inside another square, so it reads as a diamond floating in a frame. It is made from one center square and four corner triangles, cut from two corner squares, cut once corner to corner.

How many squares do I need for square in a square blocks?

Each block needs 1 center square and 2 corner squares, which make 4 corner triangles. For example, 10 blocks need 10 center squares and 20 corner squares, which make 40 corner triangles.

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