Right and Left Quilt Block Pattern

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How to Sew a Right and Left Quilt Block

The Right and Left quilt block is a classic design using half-square triangle units arranged in a mirrored pattern to create a bold directional effect. By simply rotating the HST units, you can create a variety of striking designs — it's a wonderful block for quilters of all skill levels!

How to Make the Block

This block is built entirely from half-square triangle (HST) units. Make your HSTs using the no-bias technique below, then arrange them in a mirrored right-and-left pattern. Rotate and flip the units to achieve the directional design shown in the block photo above.

No-Bias 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 Seams

Press the seam 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.

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.