If you’ve ever wondered how to make a split quarter square triangle quilt block, you’re in the right place. This versatile block adds movement and complexity to your quilts, but it’s easier to sew than it looks.

In this tutorial, you’ll learn exactly how to cut, piece, and press your block for crisp points and clean lines—no guesswork required.

The Split Quarter Square Triangle Quilt Block is a variation of the Quarter Square Triangle block, which is also referred to as the Hour Glass quilt block.

What is a split quarter triangle?

A Split Quarter triangle quilt block is that one half of the block is one fabric, and the other half of the block is two different fabrics. It’s made with half square triangle blocks.

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Is it hard to make?

No. With accurate cutting and careful pressing, it’s beginner-friendly.

The block contains one half-square triangle and two quarter-square segments to complete the square unit. This is used in many star quilt blocks, such as the Air Castle Quilt Block.

RELATED: Air Castle quilt block

What you’ll learn:

How to cut fabric for accurate triangle units
How to assemble a split quarter square triangle block
How to trim blocks to the correct size
How to avoid common mistakes

Split quarter square triangle finished block graphic

Split Quarter Square Triangles Fabric Calculator

Since this block is partially a half square triangle, and partially a quarter square triangle, we’ll use the same calculations. For the half that is one fabric (see fabric 1 above), cut squares that are 7/8″ larger than the finished size. For the half that are two fabrics (see fabrics 2 and 3 above), cut squares that are 1-1/4″ larger than the finished size. Here is a chart with common sizes:

To make 4 finished blocks, cut the following:
2″ finished size: Cut 1 square each from two fabrics at 3-1/2″ for quarter squares; cut 2 squares at 2-7/8″ for half squares.
3″ finished size: Cut 1 square each from two fabrics at 4-1/4″ for quarter squares; cut 2 squares at 3-7/8″ for half squares.
4″ finished size: Cut 1 square each from two fabrics at 5-1/4″ for quarter squares; cut 2 squares at 4-7/8″ for half squares.
5″ finished size: Cut 1 square each from two fabrics at 6-1/4″ for quarter squares; cut 2 squares at 5-7/8″ for half squares.
6″ finished size: Cut 1 square each from two fabrics at 7-1/4″ for quarter squares; cut 2 squares at 6-7/8″ for half squares.
And, so on . . .

The unfinished size for each of the blocks above will be 1/2″ larger than the finished size. Sew them together with a 1/4-inch seam allowance.

Quick start

Cut fabric squares
Make half square triangles
Turn into quarter square triangles
Press and trim to size

Now, let’s walk through it step-by-step.

Four (4) finished quilt blocks

How to Make the Split Quarter Square Triangle Quilt Block

Prep Time: 10 minutes

Active Time: 20 minutes

Total Time: 30 minutes

Difficulty: Intermediate

The Split Quarter Square Triangle quilt block is a variation of the Quarter Square Triangle and can be used as a stand-alone block or in combination with other blocks.

This is my preferred method to make this quilt block as you aren't trying to sew bias edges together. You sew along both sides of a drawn diagonal to make the diagonal seam. Bonus: there is very little fabric waste.

No special rulers are needed!

Here is our free tutorial to make the split quarter triangle block:

No Ratings

Materials

Three (3) different fabrics
Thread

Tools

Sewing machine
Iron
Ironing Board
Rotary cutter
Cutting mat
Quilters Rulers
Marking tool, I used a Frixion pen

Instructions

Step 1: Cut your fabric

Use your quilting ruler and rotary cuter to cut your fabrics according to the cutting chart above. I made 3" finished quilt blocks, so I cut two fabrics at 4-1/4" and two squares from the third fabric at 3-7/8".

Step 2: Make half-square triangles

Start by making half-square triangles from your larger cut squares. These will make the quarter triangle side of the block. Using a removable fabric marker, draw a diagonal line on the wrong side of one fabric.

Layer on top of the other larger cut square right sides together and sew 1/4" from the diagonal line. I use the 1/4-inch presser foot to make sure I sew an accurate seam.

Turn and sew 1/4" from the other side of the marked line.

Cut along the marked line to form two squares. These are basic HST blocks.

Press open.

Step 3: Create quarter square triangles

Mark the diagonal on the wrong side of the third fabric. Layer it on top of the pieced square with the the marked line 90 degrees from the stitched seam on the half square triangles.

Sew 1/4" on both sides of the line, just as before. Cut along the marked line.
Here is how it looks to put the four pieces together for a finished quilt block.

Notes

Before using in a quilt block, use a square ruler to trim up your block and cut off the dog ears.

The split quarter square triangle is a great building block for many popular patchwork designs and patterns.

Recommended Products

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Common Mistakes

Seam allowance off – leads to mismatched points
Not trimming units – blocks won’t fit together

Frequently asked questions

Do I need special rulers?
No, but a square ruler helps with trimming accuracy.

Can beginners make this block?
Yes. It builds on basic half-square triangle skills.

Why is my block twisted or uneven?
Likely from stretching fabric while pressing or cutting.

Can I chain piece these?
Yes, and it speeds things up significantly.

Tips and ideas for making the split quarter square triangle quilt block

This method makes two blocks at a time. The two blocks are mirror images of each other. You may need to make more than you need to get the layouts and colors right for your finished quilt block.
Use charm packs or layer cakes to get started on these blocks.
Pay attention to your fabric choices. To make the design pop, use different contrasting fabrics – either color choices or designs or both.
When trimming the finished squares, where the small triangles meet should be in the center of the block, the center point and be at a 45-degree line with the other half of the block.

The split quarter square triangle quilt block is one of those designs that looks intricate but becomes second nature once you’ve made a few. With careful cutting, accurate seams, and a little trimming, you’ll get crisp points and a block that fits beautifully into your quilt. Try it with bold contrasts or subtle tones—the design changes completely with your fabric choices.