Square-in-a-Square Calculator
Type the finished unit size, get the center square and the corner squares to cut, how to slice them, and the yardage for as many as you need. Then watch the unit go together, step by step.
Type the finished unit size. The center and corner squares fill in right away. Add a count for the yardage of each fabric.
What a square-in-a-square is
A square-in-a-square is a square block with a smaller square set on point in the middle and a triangle filling each of the four corners. It looks like a diamond inside a box. It shows up everywhere: on its own as the economy block, as the center of a sawtooth star, in the middle of medallions and on-point settings, and as the classic way to frame a single fussy-cut motif so it floats in a contrasting field. The whole unit is two shapes, a plain center square and four half-square-triangle corners, which is why it’s quick to cut and quick to teach.
Questions people ask
Where does the center size come from?
The center square sits on point, and its diagonal has to reach across the whole unit, so its diagonal equals the finished unit size. Working back, a square with diagonal F has a side of F ÷ √2, and you add ½″ for the two ¼″ seams. It's rounded up to the nearest ⅛″ so it lands on a ruler mark; that makes the center a hair large, which is fine, it gets squared up with the corners.
Why cut two corner squares, not four triangles' worth?
Each corner is a half-square triangle, and one square cut once on the diagonal gives two of them. Four corners therefore come from two squares. Cutting the square and then slicing it, rather than trying to cut triangles directly, keeps the straight grain on the unit's outer edges and the stretchy bias edge on the seam that gets sewn down.
These don't match my pattern's numbers.
Turn off 'cut corners a little big.' With it off the corner square is the exact chart size (a 4″ unit gives 2⅞″ corners); with it on it's cut slightly larger so you can trim the finished unit perfectly square, which is the reliable way to work because the corner seam is on the bias. The center square is the same either way. Both the cut and the exact corner size are shown.
Is a square-in-a-square the same as an economy block?
The single round here, one center plus four corners, is the square-in-a-square unit, and it's the heart of the economy block. A full economy block usually nests a second round of corners around this one; run the calculator again using this unit's finished size as the new 'center on point' to size that outer round. It's also the center of a sawtooth star, the middle of many medallions, and a great way to frame a fussy-cut motif.
Is this the same math as TideStitch?
Yes. The app builds this unit from the same pieces, a plain center square and half-square-triangle corners, using the same cut rules and rounding. This page assumes a ¼″ seam.