Quarter Square Triangles Tutorial

Quarter square triangle blocks are pretty versatile little units that are handy to have in your sewing repertoire.

A variety of quarter square triangles

Have you ever made half square triangle (HST) blocks? Quarter square triangles are as simple as making those twice! And depending on what color combinations of HST you pair together you can completely change the look of the block!

Quarter square triangle graphic chart

Pairing two of the same HST together makes the hourglass block.

Pairing two different HST makes scrappy looking blocks.

Pairing one HST with one solid block makes split quarter square blocks (also called a 3-patch quarter square triangle).

Please note that this will make two mirror images, so keep that in mind when you’re planning out your design.

Quarter Square Triangle Block

Start by determining the size block you need to cut by adding 1½” to the finished size. This will give you a little extra for trimming. If you happen to be perfect at sewing and pressing you can add 1¼” but I find that I’m always a little bit off so I prefer to trim. It makes your quilt go together so much smoother.

Quarter square triangle math cheat sheet chart

For my example my finished block measured 1″ so I started with 2½” blocks.

Start by making a HST. Pair your blocks right side together and draw a line along the diagonal on the back of one block.

Sew a ¼” seam along each side of the diagonal.

Cut along the diagonal and press the seams to the darker side.

This will give you two identical HST.

By repeating this process again using two HST we’ll end up with our block of four. Pair two HST right sides together, paying close attention to the color orientation. For an hourglass block the opposite colors should be on top of each other.

Draw a diagonal on the back of one HST making sure it is perfectly perpendicular to the seam. Don’t worry if the corners don’t match perfectly – since we’re trimming as long as it’s close enough we’ll be able to square it up.

If you want to make a split quarter square block you do the same as above – the only difference is that you’ll be pairing a HST with a plain square. Since the square will be slightly larger, center the HST.

If you pressed the seams to one side they will nicely nest together. If the seams were pressed open just pay careful attention that the diagonals line up and pin close to the diagonal to prevent shifting as you sew.

Since fabric tends to shift as you sew, if you have the top seam facing toward the foot the presser foot will push the seams together, locking them in place.

Again sew a ¼” seam along each side of the diagonal and cut along the diagonal.

If you started with your seams pressed to one side you can make your block nice and flat by pressing half the seam allowance up and the other half down, spinning the center like a little pinwheel. It sounds a bit confusing so let’s look at an example to see how this works. For my block below, instead of pressing the pink and white both in the same direction I’m going to press the pink to the left and the white to the right. I needed to remove a couple stitches from the seam to allow them to lie in opposite directions.

Then I did the same with the gray and black seam. Now all four sections in the center are separated.

Going in a circle, press each section of the seam in the same direction like a pinwheel. In mine the seams are all pressed down in a clockwise direction and the middle spins to lay flat.

Trimming

To keep everything properly centered we need to line up the center of the block with half the measurement of the unfinished block. For example, since I will be cutting my block to 1½”, I need to center the block at ¾”. Also line up the diagonal with the 45 degree mark on your ruler. This will ensure that the diagonal seams are in the corners of the block.

Trim the rest of the sides using the same method. If you have a square ruler with the diagonal mark in the corner you can actually trim two sides at a time, but since I don’t currently have one I trim one side at a time.

Quarter square triangles are a common block found in many quilt patterns and they are easier than they look!

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