How to Make a Split Quarter Square Triangle Quilt Block

This quilt block is made using split quarter square triangles. Try saying that three times fast! Although the name sounds complicated, the block is created from one simple unit that repeats throughout the design. I chose two colors for my triangles and black for the fabric that zigzags through the finished block. Once I learned how to arrange the units correctly, the block came together quickly. Four completed units create one quilt block that finishes at approximately 10 1/2 inches square.

What You’ll Need

For each set of four split quarter square triangle units, I use:

• One 4-inch square in my first color
• One 4-inch square in my second color
• Two 3 1/2-inch squares in my zigzag color

I used black for the zigzag portion of my block, but you can choose any color that creates enough contrast with your other two fabrics.

Step 1: Make the Half Square Triangles

I begin by placing my two 4-inch colored squares right sides together.

I draw a diagonal line from one corner to the opposite corner on the back of one square. Then, I sew a seam 1/4 inch away from each side of the drawn line.

Once both seams are sewn, I cut directly along the drawn line. This gives me two half square triangle units.

I open the units and press the seams flat.

Step 2: Add the Zigzag Fabric

Next, I pair each half square triangle with one of my 3 1/2-inch black squares, placing the fabrics right sides together.

The first diagonal seam from my half square triangle is already visible, but I ignore that seam. This time, I draw a new diagonal line in the opposite direction so that it crosses the original seam.

I sew 1/4 inch away from both sides of this new diagonal line.

Step 3: Cut the Split Quarter Square Triangles

I cut directly along the new drawn line and open the pieces.

The black fabric forms half of each unit, while the other half is divided between my two original colors. This creates the split quarter square triangle.

After repeating the process with both half square triangles, I have four split quarter square triangle units.

Step 4: Separate the Units

The four units are not all identical. I receive two units with one orientation and two units with the opposite orientation.

To keep everything organized, I place the units with the black triangles pointing toward the same corner. I then separate them into two piles based on where my colored triangles appear.

When I am making several blocks, I make a large batch of these units and stack each orientation in its own pile. This makes the final layout much easier.

Step 5: Arrange the Four Units

To create the repeating unit, I use two split quarter square triangles from each pile.

There are several ways to rotate these pieces, so I take my time arranging them. I position the four units so that the black sections create the zigzag design and the colored triangles form the surrounding pattern.

Once I am happy with the arrangement, I sew the top two units together and the bottom two units together. Then, I sew those two rows together to complete the unit.

Step 6: Complete the Quilt Block

I make four identical units and arrange them together to create the full quilt block.

After sewing the four units together, my finished block measures approximately 10 1/2 inches square.

This design looks intricate, but it comes together surprisingly quickly once I understand how to make and organize the split quarter square triangles. The small unit simply repeats to create the larger pattern, making this a fun block to experiment with using different colors and levels of contrast.

I hope you give this block a try. Be sure to follow Sewing Parts Online on Facebook, subscribe to our YouTube channel, and, as always, happy sewing!