How to Use Half Square Triangle Calculator
The Half Square Triangle Calculator handles every common HST math question.
- Choose Known Input — leg, hypotenuse, area, or perimeter.
- Enter the Value — Use inches or centimeters.
- Read the Result — The calculator outputs leg, hypotenuse, area, perimeter, unfinished block size (leg + 7/8 in), and finished block size (leg − 1/2 in).
Formula & Theory — Half Square Triangle Calculator
hypotenuse = leg × √2
area = leg² ÷ 2
perimeter = 2 × leg + hypotenuse
unfinished = leg + 7/8 in
finished = leg − 1/2 in| Symbol | Meaning |
|---|---|
| leg | Cut size of the square’s side |
| hypotenuse | Long edge of the triangle (diagonal cut) |
| area | Triangle area |
| perimeter | Triangle perimeter |
| unfinished | HST block size before trimming |
| finished | HST block size after sewing into another row |
Two-at-a-Time Method
starting_square = finished + 7/8 in (for two HSTs from one pair)Use Cases for Half Square Triangle Calculator
- Quilt Block Drafting — Pinwheel, flying geese, ohio star.
- Pattern Conversion — Convert imperial patterns to metric for international quilters.
- Math Education — Demonstrate the Pythagorean theorem in a tangible way.
- Scrappy Quilting — Quickly resize HSTs to use up leftover fabric.
- Pre-Cut Planning — Decide whether your charm packs fit the design.
The Half Square Triangle Calculator turns one number into a complete cutting plan.