Half-square triangle (HST) calculator

How each method works

All three methods use two squares, one of each fabric, placed right sides together with a ¼ in seam.

• 2 at a time: draw a diagonal line, sew ¼ in either side of it, and cut on the line. Easy and accurate.
• 4 at a time: sew ¼ in in from all four edges, then cut on both diagonals. Fast, but the outer edges of each HST are on the bias, so they stretch. Handle gently and starch first.
• 8 at a time: draw both diagonals, sew ¼ in either side of each, then cut through the middle horizontally and vertically and along both diagonals. Great for lots of matching HSTs.

The formulas

2 at a time: cut square = finished size + ⅞ in
4 at a time: cut square = (finished size + ½ in) × 1.414 + ½ in
8 at a time: cut square = 2 × (finished size + ⅞ in)
Every HST before sewing in (unfinished) = finished size + ½ in

Example: for 3 in finished HSTs made 2 at a time, cut 3⅞ in squares. Twenty HSTs need 10 squares of each fabric. Each HST should measure 3½ in before it's sewn into the quilt.

The 4 at a time size rarely lands on a ruler line, so the calculator rounds it up to the next ⅛ in. You then trim each HST to the unfinished size.

Tips for accurate HSTs

• Many quilters cut a little bigger and trim. The calculator's "with trimming room" size adds ¼ in; after sewing, trim each HST to the unfinished size with the diagonal line of your ruler on the seam.
• Press seams before trimming, either open (flatter) or toward the darker fabric (easier to nest).
• A scant ¼ in seam, a thread or two narrower than ¼ in, makes up for the fold of fabric at the seam.