Half-Square Triangle quilt block
One square, one diagonal, two triangles. The half-square triangle is the most-used unit in all of pieced quilting, and worth getting exactly right before anything else.
Also known as HST, Triangle Square.
Every triangle-based block in this library resolves into HSTs somewhere. Their dominance comes from a simple fact: two squares layered and stitched either side of a drawn diagonal produce two identical units with no triangle cutting at all, which is faster and more accurate than handling bias-cut triangles.
Half-Square Triangle cutting chart
Cut sizes include a ¼″ seam allowance: ½″ on squares and rectangles, ⅞″ on half-square triangles, and 1¼″ on quarter-square triangles. Pick a finished block size:
| Fabric | Shape | Cut size | Qty | Notes |
|---|---|---|---|---|
| Background | HST square | 6⅞" × 6⅞" | 1 | cut once on the diagonal → 1 triangle |
| Dark | HST square | 6⅞" × 6⅞" | 1 | cut once on the diagonal → 1 triangle |
| Fabric | Shape | Cut size | Qty | Notes |
|---|---|---|---|---|
| Background | HST square | 9⅞" × 9⅞" | 1 | cut once on the diagonal → 1 triangle |
| Dark | HST square | 9⅞" × 9⅞" | 1 | cut once on the diagonal → 1 triangle |
| Fabric | Shape | Cut size | Qty | Notes |
|---|---|---|---|---|
| Background | HST square | 10⅞" × 10⅞" | 1 | cut once on the diagonal → 1 triangle |
| Dark | HST square | 10⅞" × 10⅞" | 1 | cut once on the diagonal → 1 triangle |
| Fabric | Shape | Cut size | Qty | Notes |
|---|---|---|---|---|
| Background | HST square | 12⅞" × 12⅞" | 1 | cut once on the diagonal → 1 triangle |
| Dark | HST square | 12⅞" × 12⅞" | 1 | cut once on the diagonal → 1 triangle |
| Fabric | Shape | Cut size | Qty | Notes |
|---|---|---|---|---|
| Background | HST square | 15⅞" × 15⅞" | 1 | cut once on the diagonal → 1 triangle |
| Dark | HST square | 15⅞" × 15⅞" | 1 | cut once on the diagonal → 1 triangle |
How it goes together
Draw a diagonal on the lighter square, layer with the darker, stitch a quarter inch either side of the line, cut on the line, press. Two units per pair of squares. The eight-at-a-time method scales this up considerably.
Tips
- Cut squares ⅞ inch larger than the finished size for the two-at-a-time method, then trim to exact size.
- Trimming is not optional if you want points to survive. A specialist square-up ruler pays for itself in one quilt.
- Press toward the dark, or press open if you are about to sew many HSTs together — open seams distribute bulk better in dense blocks.
How much fabric for a Half-Square Triangle quilt?
Yardage for a whole quilt of Half-Square Triangle blocks, computed the way the studio does it — every piece packed across a 40″ usable width with 10% added for waste.
| Quilt size | Blocks | Finished | Top fabric | Backing | Binding |
|---|---|---|---|---|---|
| Baby 36×48 | 12 | 36" × 48" | Background ⅞ yd · Dark ⅞ yd | 2½ yd | ⅜ yd |
| Throw 60×72 | 30 | 60" × 72" | Background 2 yd · Dark 2 yd | 3⅞ yd | ½ yd |
| Queen 90×108 | 72 | 96" × 108" | Background 4¾ yd · Dark 4¾ yd | 8¾ yd | ⅞ yd |
What it looks like in a quilt
A single block only tells you half the story. Set sixteen of them together and the secondary pattern appears where the blocks touch:
Half-Square Triangle questions
What size squares do I need for a 3 inch finished HST?
Cut two squares at 3⅞ inches. That is the finished size plus ⅞ inch, and it yields two units.
Should I press HST seams open or to the side?
To the dark side for strength and to help points nest; open when many HSTs meet, to reduce bulk. Both are correct — it depends what the unit joins next.
What is the eight-at-a-time HST method?
Two larger squares are marked with both diagonals, stitched around all four sides, then cut apart on both diagonals and both centre lines, yielding eight identical HSTs from one pair of squares.