Half-Square Triangle Calculator

Your details

The finished dimension of one side of the completed half-square triangle block, after all seams are sewn and the block is sewn into the quilt top.
in
Total number of finished half-square triangle blocks your project requires.
HSTs
2-at-a-time uses one diagonal seam per pair. 4-at-a-time sews the perimeter and cuts both diagonals. 8-at-a-time draws two diagonals on a larger square and produces eight HSTs from one pair.
Usable width of your fabric after removing selvedges. Fat quarters are typically 18" x 22"; quilting cotton is usually 42"-44" wide.
in
Cut square size
3.875

The size of each fabric square to cut before sewing (includes seam allowance).

Cut size (fraction)3 7/8"
Unfinished size3.5
Pairs of squares to cut12
Squares per colour12
HSTs produced24
Squares per strip10
Strips per colour2
Yardage per colour0.25

You need 24 HSTs - cut squares at 3.88 in.

  • Cut each fabric square to 3.88 in using the 2-at-a-time method.
  • Budget at least 0.25 yd of each fabric colour, not counting borders or binding.
  • The 2-at-a-time method draws one diagonal line, sews a 1/4" seam on each side, then cuts along the line. The straight grain stays on the outside edge.

Next stepAfter sewing, trim each block to the unfinished size using a square ruler with a 45-degree angle line before joining blocks together.

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