Quilt Pattern Math for Triangles: Three Common Cases Explained

Triangle math is where quilt pattern writing often starts to feel more complicated than it needs to be. In this Tech Tip Tuesday, I walk through the underlying math behind several common triangle situations. We’ll look at three specific cases: free triangles sewn on the diagonal, setting triangles for on-point quilts, and triangles cut by the strip. For each one, I explain what’s actually happening with seam allowances and angles, and share simple, practical rules that give you workable sizes you can trim accurately. This is meant to help you understand the logic behind the math so you can either apply it confidently. If you'd prefer not to mess with the algebra, check out my free quilt shape calculators: https://mathlessquilts.com/freecalculators 00:00:00 Why triangle quilt math feels harder 00:01:05 Free triangles sewn on the diagonal 00:01:25 Why seam allowances get tricky on diagonals 00:02:22 Simple sizing rule for free triangles 00:03:05 Setting triangles for on-point quilts 00:03:25 Avoiding bias edges on quilt borders 00:04:27 Quarter vs half setting triangles 00:05:00 Rounding and trimming strategy 00:05:18 Triangles cut by the strip 00:05:52 Strip triangle math formula explained