Half Square Triangle Arrangement Quilt Block Pattern

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How to Sew a Half Square Triangle Arrangement Quilt Block

Sewing an HST arrangement quilt block involves cutting and piecing fabric squares to create a design made up of triangles. The arrangement of those triangles is what creates the unique pattern.

1. Choose your fabric: Select two or more fabrics that complement each other and will look good together in a quilt block.
2. Cut the fabric squares: Cut squares 1" larger than the finished block size. For a 6" finished block, cut two 7" squares from each fabric.
3. Mark the diagonal: Draw a diagonal line from corner to corner on the wrong side of one square using a fabric pen or pencil.
4. Layer the squares: Place the two squares right sides together, with the marked square on top.
5. Sew along the diagonal: Sew a ¼" seam on both sides of the marked line.
6. Cut along the line: Cut along the marked line with a rotary cutter to create two HST units.
7. Press open: Press the HSTs open with an iron, seam allowance toward the darker fabric.
8. Trim: Trim the HSTs to the desired size, keeping them square.
9. Arrange: Arrange the HSTs in your desired pattern — by color, rotation, or randomly.
10. Sew together: Sew the HSTs together into rows, matching seams with a ¼" seam allowance, then join the rows.
11. Press the block: Press the completed block carefully without stretching the fabric.

Your HST arrangement quilt block is complete! Repeat to make more blocks and sew them together into a beautiful quilt.

Half-Square Triangle (HST) Technique

This technique eliminates the need to directly manipulate the stretchy bias of the triangle. It uses two easy-to-cut squares and produces two HSTs at once.

Step 1: Draw the Diagonal Line

On the back of the lighter fabric, draw a pencil line diagonally from corner to corner.

Step 2: Sew Both Sides of the Line

Stack a pair of light and dark squares right sides together. Sew a ¼" seam allowance on each side of the line.

You will end up with something like this:

Step 3: Cut Along the Diagonal Line

Step 4: Press the Seam

Press the seam together to set it, then press toward the darkest fabric.

Step 5: Trim to Size

Line up the 45° diagonal angle on your ruler with the seam, then carefully trim with a rotary cutter.

Nine Patch Technique

The secret to a perfect nine patch is pressing seams so they butt together neatly when joined.

Method 1: Individual Squares

1. Cut 5 A squares and 4 B squares in the required size.
2. Using chain piecing, join a B square to 3 of the A squares, right sides together, with a ¼" seam allowance. No need to press just yet.

The result will be:

3. Take the remaining A and B squares and, using chain piecing, join them to these units, right sides together, with a ¼" seam allowance.

Your result will be:

Method 2: Strip Piecing (Faster)

Cut A and B strips to the appropriate width and join them into A/B/A and B/A/B units. You will need twice the length of B/A/B strips. Sew right sides together with a ¼" seam allowance and press every seam toward the dark fabric.

Cut across your pre-joined strips to create the units needed for the nine patch:

You will achieve the same result as Method 1, but faster. For a standard nine patch, the width of the unit cut from pre-joined strips equals the width of the original strips.

Assembling the Nine Patch

1. Press all seams toward the dark fabric so they butt up neatly.
2. Join the B/A/B units to your A/B/A units with butted seams, right sides together, with a ¼" seam allowance.
3. The direction of the final central seam is optional — press to facilitate butting the seam joints based on the block's placement in the larger quilt.

Wider Application

Just like the four patch, you can apply this methodology to all kinds of nine patch blocks. As long as a block has an underlying 3×3 grid, the basic principle applies. Keep pressing seams in pairs of opposite directions and piecing will be smooth sailing.

Try these blocks — each has an underlying 3×3 grid and can be pieced as a nine patch:

Sometimes it's not obvious which direction is “dark” with complicated blocks. Just remember the basic pressing plan:

How to Resize Quilt Blocks

The first step in modifying any quilt block is to decide on your finished block size. You can base this on doubling a pattern, cutting it in half, or working with your available fabric.

Note: When working from a pattern's cutting instructions, remove the seam allowance before scaling. For example, if your pattern calls for 3½″ squares, subtract the seam allowance (½″), double the finished size (3″ → 6″), then add the seam allowance back (½″) — giving you a 6½″ cut piece.

Resizing Square Blocks

Add ½″ to your finished block measurement. For a 4″ finished square, cut a 4½″ square of fabric.

Resizing Rectangular Blocks

Add ½″ to both the length and width. To double a 3″ × 4″ block, cut a 6½″ × 8½″ rectangle.

Resizing Half-Square Triangle Blocks

Add 7/8″ to the desired finished block size. For a 4″ finished HST block, cut 4⅞″ squares.

Resizing Quarter Square Triangle Blocks

Add 1¼″ to the desired finished block size. For a 4″ finished block, cut 5¼″ squares.