Quarter Square Triangle Tutorial

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Learn to make quarter square triangle units faster...no making HSTs first! Make split quarter square triangles with ease!

Picture of quarter square triangle units without marking for half square triangles.quarter square triangle units cut without marking

There are many ways to make quarter square triangles (QSTs). Today, a lot of quilters make half square triangles first. However, this is not necessary.

You can cut two squares, right sides together, on each diagonal to make four QST units.

The placement of fabric and the side of the triangles that you stitch together
determines whether you get split quarter square triangles, non-mirror QSTs or hourglass units.

The instructions below demonstrate how to obtain each.

Quarter Square Triangle Math

The math for making quarter square triangles is finished size (FS) unit plus one and a quarter inches. For example, in a 12 inch block the finished size QST unit needed is 4 inches. To make the QSTs, from two different fabrics cut 1 (5 1/4 inch) square.

Finished Size QST Unit + 1 1/4 inches

If you like, make oversized units and then trim them to size. Add 1 1/2 inches to the finished size QST. This is how I make them.

Quarter Square Triangle Cutting Chart

Here are measurements for some common sizes of QST units used to make star quilt blocks.

In this tutorial the fabrics are designated as follows:

  • Fabric A = blue print
  • Fabric B = background (med blue variegated)

Quarter Square Triangle Instructions

WOF = Width Of Fabric
Seams are 1/4 inch unless otherwise noted.

Step 1 Spray and press all squares with a starch alternative pressing solution.

Place Fabric A square right side up and align Fabric B square right side down on top of it.

Quarter Square Triangle Tutorial Step 1: Place QST squares right sides together, background square on top.

Step 2 Place a quilting ruler on the left leaning (\) diagonal axis of the squares. Use a rotary cutter and make a cut from corner to corner.

Quarter Square Triangle Step 2: place a quilting ruler on the left leaning (\) diagonal axis and use a rotary cutter to make a cut along it.

Step 3 Keep the two halves of the squares together. Place a quilting ruler on the right leaning (/) diagonal axis of the squares. Make a cut from corner to corner.

Quarter Square Triangle Step 3: place a quilting ruler on the right leaning (/) diagonal axis and use a rotary cutter to make a cut along it.

You've cut four quarter square triangle pairs.

Quarter Square Triangle: four quarter square triangle pairs are cut.

Step 4 Place the QST pairs so that the outside edges are oriented in the 6 o'clock position.

Quarter Square Triangle Step 4: Place the QST pairs so that the outside edges are oriented in the 6 o'clock position.

Sewing Quarter Square Triangles

The QST units are ready to be sewn together.

Below are instructions on how to sew them together to get the units that you want: non-mirror QSTs, hourglass units or split quarter square triangles.

Non-Mirror Quarter Square Triangles

To get QSTs that are all the same (non-mirror or non-split), stitch each QST pair along the same edge.

Quarter Square Triangle: In Photo 1, the left edges are stitched together. In Photo 2, the right edges are stitched together.Photo 1
Quarter Square Triangle: In Photo 1, the left edges are stitched together. In Photo 2, the right edges are stitched together.Photo 2

Compare the above photos. Both were stitched with the background Fabric B on top. In Photo 1, the left edges are stitched together. In Photo 2, the right edges are stitched together. Notice the right-leaning versus left-leaning diagonal axis.

Before stitching, check that your fabric placement will be in the correct position once the units are stitched together.

The fabric that's on top when going under the needle will be on top when the unit is pressed open.

Hourglass Quarter Square Triangles

To make hourglass units, stitch together two units along the same side edges.

Quarter Square Triangle Tutorial: Stitching together two units along the same side edges allows you to make hourglass units.

Split Quarter Square Triangles

To get QSTs that are split (mirror image), stitch a QST pair along the left edge and one along the right. Below, the units are sewn with background Fabric B on top.

Quarter Square Triangle Tutorial: To get  split (mirror image), stitch two QST pairs along the left edge and two along the right. In the pic the units are sewn with background Fabric B on top.

These split quarter square triangles are sewn with background Fabric B on the bottom.

Quarter Square Triangle Tutorial: split quarter square triangles are sewn with background Fabric B on the bottom.

Blocks With Quarter Square Triangle Units

Knowing how to make a quarter square triangle unit this way requires no marking. And, when it comes to the hourglass units you don't have to make half square triangles first.

This method comes in handy when making star quilt blocks such as the Double Friendship, Duck Tracks or Ohio Star. The quarter square triangle is a versatile quilt block unit!

If you prefer another method see how to use 1/4 square triangle ruler or the 3 Patch Quarter Square Triangles Tutorial.

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