Pinwheels & triangles · Confident beginner

Half-Square Triangle quilt block

A square made of two right triangles. The basic unit behind most triangle blocks. Also called Triangle Square.

Half-Square Triangle: main and background. A 1 × 1 grid.

Cutting chart by block size

Fabric	Cut	Size	Then
Main	1 square	4 7/8" × 4 7/8"	1 triangles (cut once on the diagonal)
Background	1 square	4 7/8" × 4 7/8"	1 triangles (cut once on the diagonal)

Fabric	Cut	Size	Then
Main	1 square	6 7/8" × 6 7/8"	1 triangles (cut once on the diagonal)
Background	1 square	6 7/8" × 6 7/8"	1 triangles (cut once on the diagonal)

Fabric	Cut	Size	Then
Main	1 square	8 7/8" × 8 7/8"	1 triangles (cut once on the diagonal)
Background	1 square	8 7/8" × 8 7/8"	1 triangles (cut once on the diagonal)

Fabric	Cut	Size	Then
Main	1 square	12 7/8" × 12 7/8"	1 triangles (cut once on the diagonal)
Background	1 square	12 7/8" × 12 7/8"	1 triangles (cut once on the diagonal)

Cut the pieces in the chart above. All measurements include a 1/4" seam allowance.
Cut the squares marked "cut once" in half on the diagonal. Each gives two triangles. Sew them to their neighbours along the long edge first and press toward the darker fabric.
Lay the pieces out as in the diagram and sew them together, matching the center.
The block should measure 12 1/2" now and 12" once it is sewn into the quilt.

Yardage for a Half-Square Triangle quilt (12" blocks)

Quilt size	Blocks	Finished size	Main	Background	Border & binding	Backing
Baby	3 × 4 (12)	42" × 54"	7/8 yd	7/8 yd	1 yd	3 1/2 yd
Lap	4 × 5 (20)	54" × 66"	1 5/8 yd	1 5/8 yd	1 1/8 yd	4 1/4 yd
Throw	5 × 6 (30)	66" × 78"	2 yd	2 yd	1 3/8 yd	5 yd
Twin	6 × 8 (48)	78" × 102"	3 1/4 yd	3 1/4 yd	1 3/4 yd	9 1/4 yd
Queen	8 × 8 (64)	102" × 102"	4 3/8 yd	4 3/8 yd	1 7/8 yd	9 1/4 yd
King	9 × 9 (81)	114" × 114"	5 5/8 yd	5 5/8 yd	2 1/8 yd	10 1/4 yd

Blocks side by side with a 3" border, 2 1/2" binding, 42" usable width and 10% extra.

A throw quilt of 12" Half-Square Triangle blocks in each setting.

Setting	Blocks	Finished size	Extra fabric
Side by side	30	66" × 78"	–
With sashing	20	60" × 74"	Sashing 7/8 yd, Cornerstones 1/8 yd
Alternating plain blocks	15 pieced + 15 plain	66" × 78"	Plain blocks 2 yd
On point	18	57" × 74"	Setting triangles 1 1/2 yd

1. Your fabrics (tap a fabric, then choose a sample or your own photo)

2. Block

3. Quilt size

4. Block size

5. Setting

Border

Fabric	Yardage	Cut

Based on 42" usable fabric width, 1/4" seams and 10% extra. Your photos stay on your device.

How many fabrics does a Half-Square Triangle block need?

Two: main and background. Choose a main fabric that contrasts clearly with the background so the design reads from a distance.

What size pieces do I cut for a 12 inch Half-Square Triangle?

1 main square at 12 7/8" × 12 7/8"; 1 background square at 12 7/8" × 12 7/8".

How many Half-Square Triangle blocks for a lap quilt?

20 blocks at 12", set 4 by 5 with a 3" border, make a 54" × 66" quilt.

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