How to Make a Three-Part Triangle Quilt Block

Quilt Tutorial: How to Make a Three-Part Triangle Quilt Block

A 3-part triangle quilt block can be used to make many interesting designs in a quilt. It is a relative of the quarter-square triangle quilt block. (QST) Instead of starting with two Half-Square Triangle (HST) quilt blocks, you start with one. Here is how to make it.

Quilt Tutorial: How to Make a Three-Part Triangle Quilt Block
To demonstrate this technique, I am starting with (4) squares, a dark and a light 3-1/2″ square and two light 3″ squares. I have drawn a line on the diagonal of all the light squares. Because I started with four squares, I will end up with four blocks.
Quilt Tutorial: How to Make a Three-Part Triangle Quilt Block
Placing the two 3-1/2″ squares right sides together, I have sewn 1/4″ on both sides of the diagonal line and cut the two sides apart.
Quilt Tutorial: How to Make a Three-Part Triangle Quilt Block
I then squared up the two half-square-triangle blocks to 3″. The ruler in the picture is the Creative Grid CGR3.
Quilt Tutorial: How to Make a Three-Part Triangle Quilt Block
I placed a 3″ square right sides together with the half-square-triangle blocks.
Quilt Tutorial: How to Make a Three-Part Triangle Quilt Block
I sewed 1/4″ from either side of the diagonal line and cut apart the block.
Quilt Tutorial: How to Make a Three-Part Triangle Quilt Block
That gave me four blocks to square up to 2-1/2″. The ruler in the picture is from Quilt in a Day. I like those rulers because you can precisely line up the center and cut around the ruler. I now have (4) three-part triangle blocks.
Quilt Tutorial: How to Make a Three-Part Triangle Quilt Block
Sample Block

How to Make this block in three colors

Quilt Tutorial: How to Make a Three-Part Triangle Quilt Block
To make a three-part triangle quilt block with three colors, start with (4) squares, a dark and a light 3-1/2″ square, and two 3″ squares of the third color. I have drawn a line on the diagonal of the light squares, and on the back of the third color squares. Because I started with four squares, I will end up with four blocks.
Quilt Tutorial: How to Make a Three-Part Triangle Quilt Block
Placing the two 3-1/2″ squares right sides together, I have sewn 1/4″ on both sides of the diagonal line and cut the two sides apart. Now I will press them open and square them up to 3″.
Quilt Tutorial: How to Make a Three-Part Triangle Quilt Block
I put the third-color square right sides together with the HSTs I just made. I sewed 1/4″ on both sides of the diagonal line, then cut them apart on the line.
Quilt Tutorial: How to Make a Three-Part Triangle Quilt Block
That gave me four blocks to square up to 2-1/2″. The ruler in the picture is from Quilt in a Day. I like those rulers because you can precisely line up the center and cut around the ruler. I now have (4) three-part triangle blocks.
Quilt Tutorial: How to Make a Three-Part Triangle Quilt Block
Notice how these blocks are NOT identical. Two of them have the dark on the top and two have the dark on the side. Be careful to place the color correctly when using them in a quilt.
Quilt Tutorial: How to Make a Three-Part Triangle Quilt Block
Sample Block Border

How to Make a Three-Part Triangle Block using the Bias Beauty Method

Three-Part Triangle Quilt Block Unit Construction

In this method, you make four three-part triangle units at once – two that are mostly dark and two that are mostly light.

Start with two strips of fabric the same size. In this example, I am using two 3″ wide strips.

Three-Part Triangle Quilt Block Unit Construction

Sew them together with a 1/4″ seam. Press open. Cut (2) 5-1/2″ squares.

Three-Part Triangle Quilt Block Unit Construction

Turn one square 90 degrees and place them right sides together so the seams are perpendicular to each other. Pin the two blocks together at the seam allowance, double-checking to make sure those seams are at right angles.

Using a 1/4″ seam allowance, sew all the way around the outside of this packet. You are basically making a pillow with no way to get to the inside. Press. Cut the packet on both diagonals.

Three-Part Triangle Quilt Block Unit Construction

Open up your pieces and press. You MUST square these up. I am showing the Quilt-in-a-Day Fussy Cut ruler and the Creative Grid CGR35 below. Choose the one you like the best and use it!

Three-Part Triangle Quilt Block Unit Construction
Quilt in a Day Fussy Cut Ruler
Three-Part Triangle Quilt Block Unit Construction
Creative Grid 3-1/2″ Ruler

Yes, I know the edges of this block are on the bias. That’s why I call it the Bias Beauty method. However, it really doesn’t seem to make a difference on a block this small. I think the fact the seam is on the straight of grain and holds everything firmly together keeps this block from misbehaving. Give it a try!

Have another tip to offer? Send it to me or reply below and I will add it here.

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