Learn how to calculate setting triangles and how to construct an eye-catching on point quilt!
If youโve ever tried making a quilt thatโs set โon-pointโ you have surely needed to make setting triangles.
If you follow a pattern you normally donโt have to deal with any setting triangles formulas or calculations. But if you want to design a quilt on your own – or just like how your blocks look rotated 45 degrees – youโll need to do some triangle math.
Today weโll look into the whole theory behind setting triangles. Weโll explore what they are, how to use sew them, and of course, how to calculate setting triangles based on the dimensions of your specific quilt.
What are setting triangles in quilting?
Letโs start at the beginning and clarify what exactly are setting triangles in quilts.
As Iโve mentioned, setting triangles are used for quilts that are constructed on point.
If you look at the image below you can instantly see the difference between a straight quilt setting and an on-point quilt setting.

Straight quilt setting: the blocks are arranged vertically or horizontally. Sashing and borders may be added in between the blocks.
On-point quilt setting: the blocks are turned 45 degrees (arranged โdiagonallyโ).
As you can see in the picture, with on-point quilts, you need some fabric to fill in the gaps that occur along the edges of the quilts. And this is where setting triangles come in!
Setting triangles are the triangular pieces of fabric used to fill in the edges of a quilt when blocks are arranged on-point. They come in two types:
- Side Setting Triangles: These are used along the edges of the quilt to complete the straight edges.
- Corner Setting Triangles: These are placed in the four corners of the quilt to square off the layout.
How to calculate setting triangles?
Now on to the fun part – quilt math. Haha, I know not everyone shares my enthusiasm – but youโll be happy to learn we have a solution for you even if you hate quilt math!
There are two ways you can go about calculating setting triangles.
Option A: Setting Triangles Calculator in Quilt Geek
The fastest way to calculate setting triangles is to use the calculator in Quilt Geek, our quilting calculator app – the setting triangle calculator is coming to Quilt Geek with the next update. Stay tuned!
Option B: Do the Math Yourself
Of course, you can always do the math the old-school way. It takes some more effort, but Iโll try to make it as simple as possible.
As I explained earlier, there are two types of setting triangles – corner and side setting triangles. You need to calculate both for one quilt. Youโll always need 4 corner setting triangles. And the number of side setting triangles depends on the number of blocks youโre using.

First, letโs calculate corner setting triangles.
The corner setting triangle formula is:
(Finished block size / 1.414) + โ
Round the result up to the nearest โ
inch
This formula returns the size of the starting square you need to cut from your fabric to make two corner setting triangles.
The starting square is sub cut diagonally once to get two corner setting triangles:

For example, if your blocks are 8 inches finished, your starting square will be:
(8/1.414) + โ
= 5.658 + โ
= 6.533 โ Rounded up to 6 โ
Now, letโs look into side setting triangles.
The side setting triangle formula is:
(Finished block size x 1.414) + 1 ยผ
Round the result up to the nearest โ
inch
This formula returns the size of the starting square you need to cut from your fabric to make four side setting triangles
The starting square is sub cut diagonally twice to get four side setting triangles:

For example, for our 8 inches finished blocks, the starting square will be:
(8 x 1.414) + 1 ยผ = 11.312 + 1 ยผ = 12.562 โ Rounded up to 12 โ
How to sew setting triangles?
Now that weโve done the math and cut the setting triangles, itโs time to sew the quilt top together. Thereโs no science behind this. As always, I recommend going slow and pinning everything in place.
As opposed to going from top to bottom or left to right (as you would with straight set quilts), you will sew the quilt together on the diagonal.
First, lay out your pieces on a design wall or a large surface. Sew the blocks and setting triangles together into (diagonal) rows.

Next, attach the two remaining corner setting triangles onto the end pieces.

Finally, sew the rows together. And youโre done!

There you go! Youโve just learned how to calculate and sew setting triangles so you can go ahead and finish that on-point quilt!
Happy quilting!
Further Reading
Finish a Quilt in 3 steps
If you’re new to quilting and you’re overwhelmed with how to make a quilt from start to finish, here are the 3 basic steps to finish your quilt with links to useful tutorials:
Comprehensive beginner-friendly tutorial: How to Baste a Quilt >
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How to choose backing for a quilt >
How to plan and calculate quilt backing >
The magic diagonal quilt backing >
20+ modern pieced quilt backing ideas >
How to choose quilt batting >
Comprehensive beginner-friendly machine quilting tutorial: Machine Quilting for Beginners >
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Inspiring Straight Line Quilting Designs >
The Ultimate Stitch in the Ditch Tutorial >
Comprehensive beginner-friendly machine binding tutorial: The Ultimate Machine Binding Tutorial >
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How to get perfect quilt binding corners >
Stitch in the Ditch Quilt Binding (Looks Hand-Sewn) >
How to fix wavy binding >