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How to Sew a Hidden Square Quilt Block
The Hidden Square quilt block creates a striking optical illusion by nesting smaller square blocks within larger ones, giving the appearance of a continuous geometric pattern.
Materials Needed
- Fabric in desired colors and patterns (at least two contrasting fabrics)
- Sewing machine and quilting thread
- Rotary cutter and cutting mat
- Ruler
- Iron and ironing board
Step-by-Step Instructions
Step 1: Choose Your Fabrics
Select fabrics in colors and patterns that complement each other — one for the large square blocks and a contrasting fabric for the smaller square blocks.
Step 2: Cut the Fabric
Cut the larger square blocks to your desired size, adding ¼" for seam allowances. Cut the smaller square blocks 1" smaller than the larger blocks, also adding ¼" for seam allowances.
Step 3: Assemble the Smaller Square Blocks
Sew the smaller square blocks together in a pattern to create a larger unit. Press the seams open.
Step 4: Mark the Diagonal Line
Mark the wrong side of the unit with a pencil line, aligning the corners of the squares and the intersection of the seams.
Step 5: Add the Corner Triangle
Line up the corner of the square or triangle you will add to the corner of the unit.
Sew a seam one thread's width from the marked line — this tiny allowance makes room for the fold of the fabric so the triangle point isn't cut off. Then fold the triangle into position using the squares to assist alignment, and press.
Step 6: Trim
Trim away excess fabric to reduce bulk, leaving a ¼" seam allowance and trimming the ears.
Step 7: Assemble the Quilt Top
Arrange the blocks in your desired pattern and sew them together with a ¼" seam allowance. Press the seams open.
Step 8: Quilt and Finish
Layer the quilt top, batting, and backing fabric together and quilt as desired. Bind the edges to finish.
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.
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.
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