Half-Square Triangle Math

for designing quilt blocks

Basic Concepts

You can create 2, 4 or 8 half square triangles starting with 2 larger squares of fabric.
  1. Begin with 2 squares of fabric, right-sides facing, same size, and of a different color/pattern.
  2. Draw the solid lines with a fabric-safe pencil.
  3. Sew along the dashed lines, 1/4 an inch from the drawn lines or edges.
  4. Cut along the solid lines using a clear ruler and a rotary blade.
  5. Press the HST units with an iron, trim the dog ears, trim down to size (optional), keeping the 45° angle.
Take out some scraps and practice!

Traditional (2 HSTs) Method


Quad (4 HSTs) Method


Octo (8 HSTs) Method


Calculate Size

The result is rounded down to the nearest 1/16th
All values below are in inches.