How it works
Every method starts with two squares, one of each fabric, placed right sides together. What changes is how you sew and cut them.
2 at a time: cut square = finished + ⅞"
4 at a time: cut square = finished × 1.414 + 1¼" (rounded up to ⅛")
8 at a time: cut square = (finished + ⅞") × 2
Trim to: finished + ½"
2 at a time: draw one diagonal, sew ¼" on both sides, cut on the line. You get two HSTs with straight-grain outer edges. Many quilters cut at finished + 1" instead and trim for extra accuracy.
4 at a time: sew ¼" around all four edges, then cut on both diagonals. The × 1.414 (√2) comes from geometry: the square’s edge becomes the diagonal of each HST. Some patterns simplify this to “finished + 1¼”, but that is too small for anything bigger than a tiny HST. We use the exact formula and round up. The outer edges are on the bias, so handle them carefully.
8 at a time: draw both diagonals, sew ¼" on either side of each, then cut horizontally, vertically and on both diagonals. The cut square is twice the 2-at-a-time size.
Worked example
For 20 HSTs that finish at 3": 2 at a time needs ten 3⅞" squares of each fabric. 4 at a time needs five 5½" squares (3 × 1.414 + 1.25 = 5.49). 8 at a time needs three 7¾" squares and gives you 24, four spare.
Making hourglass units instead? Those need ¼" more than this, because they have two diagonal seams: use the quarter-square triangle calculator. Corner triangles for a square in a square block are HSTs too.
Last checked October 2026 against standard quilting and knitting math. Found a mistake? Tell us and we’ll fix it.