How to Make Half Square Triangles: 2, 4 and 8 at a Time Cut Size Charts

How to make half square triangles two at a time

1. Cut the squares. Cut one light and one dark square 1 in larger than the finished HST size, using a Olfa RTY-2/C 45mm and a square ruler such as the Omnigrid 12-1/2 in Square. For 3 in finished HSTs, cut 4 in squares.
2. Mark the diagonal. On the wrong side of the lighter square, draw a line from corner to corner with a fine marker or a Clover Chaco Liner.
3. Pair the squares. Place the marked square on the dark square, right sides together, edges aligned. Pin at the corners with Clover Fine Patchwork Pins if they slip.
4. Sew both sides of the line. Sew a scant 1/4 in seam on each side of the drawn line, using the edge of a 1/4 in foot as a guide. Chain-piece many pairs in a row to save thread and time.
5. Cut on the line. Cut exactly on the drawn diagonal with a rotary cutter. Each pair now makes two HSTs.
6. Press the seam. Press the seam toward the darker fabric, or open to reduce bulk, setting the seam first with the iron on a PQT Wool Mat 17x24.
7. Trim to the unfinished size. Align the 45 degree line of a square ruler or a slotted Bloc Loc HST Set #2 ruler with the seam and trim each HST to 1/2 in larger than the finished size, so a 3 in HST measures 3 1/2 in.

What is a half square triangle in quilting?

A half square triangle is a square unit divided on the diagonal into two triangles, usually in contrasting fabrics. The name comes from the shape: each triangle is half of a square.

Two sizes matter for every HST. The finished size is how big the unit appears once it is sewn into a quilt, after seam allowances are hidden. The unfinished size is what the HST measures before it is sewn into a block, always 1/2 in larger than finished because of the 1/4 in seam allowance on each side. Patterns usually give the finished size, and every chart below starts from it.

HSTs fit block grids exactly: multiply the finished HST size by the units across. Four 3 in HSTs in a 2 x 2 grid make a 6 in pinwheel block; a 4 x 4 grid makes a 12 in sawtooth star variation. The quilt block size calculator helps work backward from a quilt size to a block and HST size.

What size do you cut half square triangles?

Each method has its own formula. Exact cuts give the finished size with no trimming, if every seam is perfect. Trim cuts are slightly larger so you can square each unit afterward.

• Two at a time: exact = finished + 7/8 in; to trim, finished + 1 in.
• Four at a time: exact = (finished x 1.414) + 1 1/4 in, rounded up to the next 1/8 in; to trim, round that up to the next 1/4 in and add 1/4 in.
• Eight at a time: exact = 2 x (finished + 7/8 in); to trim, 2 x (finished + 1 in).

Each size has its own page with yardage and block ideas: 2 inch, 2 1/2 inch, 4 inch, 6 inch and the full HST size index. Making flying geese as well? The 2 x 4 flying geese page uses the same approach.

How do you make half square triangles 4 at a time?

The four at a time method sews around the outside of a pair of squares, then cuts both diagonals.

1. Cut one light and one dark square to the four at a time size. For 3 in finished HSTs, 5 3/4 in to trim.
2. Place them right sides together and sew 1/4 in from the edge all the way around all four sides.
3. Cut corner to corner on both diagonals, making four triangles-in-squares.
4. Press and trim each to the unfinished size, 3 1/2 in.

It is fast, because one square of each fabric makes four units. The catch: the outside edges of each HST are cut on the bias, the stretchy diagonal of the fabric. Handle them gently, press with an up-and-down motion instead of sliding the iron, and consider a light spray starch before cutting. Many quilters trim these slightly larger for that reason.

How do you make half square triangles 8 at a time?

The eight at a time method, often called the magic 8, is the favorite for making a lot of matching HSTs.

1. Cut one light and one dark square to the eight at a time size. For 3 in finished HSTs, cut 8 in squares to trim.
2. On the wrong side of the light square, draw both diagonals, corner to corner, making an X.
3. Place the squares right sides together and sew 1/4 in on both sides of both diagonal lines. That is four seams.
4. Cut the square in half horizontally and vertically through the center, making four smaller squares.
5. Cut each smaller square on the drawn diagonal line. You now have eight HSTs.
6. Press and trim each to the unfinished size.

The outside edges are on the straight grain, which makes them more stable than the four at a time method. A rotating mat such as the Olfa 17in Rotating Mat lets you make all the cuts without lifting the stack.

Which half square triangle method uses the least fabric?

It depends on the size, because squares that barely fit across the fabric waste strip width. Here is the same job, 100 HSTs finishing at 3 in, cut to trim from strips of 42 in cotton with about 40 in usable.

For 3 in HSTs, two at a time uses the least fabric because exactly 10 squares of 4 in fit across 40 in. Four at a time wastes the most, since only six 5 3/4 in squares fit per strip. The bigger difference is sewing time: eight at a time needs only 13 pairs instead of 50, so it is often the fastest. Try your own size and count in the HST calculator, and see how to calculate fabric yardage for the underlying math.

How do you trim half square triangles accurately?

Trimming is what makes HST points meet. The method is the same for every size:

1. Place a square ruler on the HST with its 45 degree diagonal line exactly on the seam.
2. Position the ruler so the unit extends a little past the unfinished measurement on two sides, then trim the right and top edges.
3. Rotate the HST, line up the freshly cut edges with the unfinished measurement lines and the diagonal with the seam, then trim the other two sides.

Rulers make a real difference. A set of square rulers such as the Omnigrid 4-Square Value Pack, with 4 1/2, 6 1/2, 9 1/2 and 12 1/2 in squares and a 45 degree diagonal, covers most sizes. A slotted trimming ruler like the Bloc Loc HST Set #2, in 2 1/2, 4 1/2 and 6 1/2 in sizes, locks onto the seam so the ruler cannot slide. Trim dozens of units on a rotating mat and good light; a daylight lamp such as the Daylight Artist Studio 2 makes the fine lines on a ruler easier to see.

What size half square triangles can you make from a charm pack or layer cake?

Precut squares are a shortcut for HSTs, since the squares are already cut. Use the trim sizes so the units square up cleanly.

A charm pack of about 42 squares makes 21 pairs, so 42 HSTs of 4 in finished by the two at a time method. A layer cake makes 168 HSTs of 4 in finished by the eight at a time method. Pair prints with a white or solid layer cake such as Bella Solids White Layer Cake for crisp contrast.

Can you cut half square triangles with a die cutter?

Yes, and for large quilts it is the fastest route. Fabric die cutters press fabric against a die with a steel blade in the shape you need, cutting several layers in one pass with the seam allowance included. AccuQuilt machines cut up to 6 layers of cotton per pass.

• The AccuQuilt GO! Me, about $107, includes HST and quarter square triangle dies for 3 in finished units.
• The AccuQuilt GO!, about $330, includes a value die with 4 1/2 in squares, 2 1/2 in squares and an HST shape.
• The electric AccuQuilt GO! Big, about $700, runs the whole AccuQuilt die range including the large 14 x 16 in dies, with a one-button motor that is easier on hands and wrists than a crank.
• The AccuQuilt GO! Big Qubed, about $3,000, bundles Qube sets for 6, 8, 9, 10, 12 and 16 in blocks, a strip cutter and mats for quilters who cut nearly everything by die.

Die cutting suits patterns built on standard sizes; rotary cutting stays more flexible for odd sizes. Compare the options in the best fabric cutting machines for quilting and AccuQuilt GO vs GO Big.