Half-Square Triangle (HST) Quilt Block

The half-square triangle is one of the oldest patchwork units in existence, documented in American quilts from the earliest years of the republic and in European patchwork going back even further. Colonial quilters knew that triangles waste fabric — cut a square diagonally and you lose the seam allowance to the cut — so early patterns often used triangles to use up scraps that couldn't make a whole square.

By the mid-19th century, HSTs were everywhere: Ocean Waves, Birds in the Air, Bear's Paw, Pinwheel, Flying Geese, and dozens of star variations all depend on HST units. The pattern is so fundamental that it appears in quilting traditions from every continent. In Japan, traditional patchwork forms use the same two-triangle construction; in England, "half-square patches" appear in broderie perse and medallion quilts from the Georgian era.

Modern quilters benefit from accurate rotary cutting and the "2-at-a-time" method — drawing a diagonal line on a square, sewing on both sides, then cutting apart — which produces two perfectly matched HSTs at once. The "8-at-a-time" method, developed in the 1990s, produces eight identical HSTs from two larger squares with a single round of stitching, making it ideal for large projects.