Side Triangle and Corner Triangle Cutting Chart

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Last Updated March 04, 2018

triangle cutting chart for setting triangles and corner triangles
Quilters use this triangle cutting chart when piecing a diagonal layout quilt. In a diagonal layout, blocks are placed on-point.

Glossary Terms for Triangle Cutting Chart

  • on-point
  • diagonal layout, diagonal setting
  • corner triangle
  • side triangle
  • finished size

First we have to understand what side and corner triangles are.  The corner triangles, shown in black, are in the corners. Side triangles, shown in gray, are along the edges.

 

Cutting Triangles from Squares

This triangle cutting chart is based on cutting squares then sub-cutting the squares into triangles.

Cut the square twice diagonally for side triangles.

setting triangle cuts from triangle cutting chart
Side Triangle Cuts

Cut the square once diagonally for corner triangles

corner triangle cuts from triangle cutting chart
Corner Triangle Cuts

Why Cut Triangles from Squares?

Squares are easy to cut. First, cut along the width of fabric. Next, sub-cut into squares. Finally, sub-cut the squares into 2 or 4 triangles. Cutting squares this way ensures the grain lines follow the outer edges of the quilt.

The picture below shows the grain lines for the side triangle cuts. These cuts put either the crosswise or lengthwise grain along the outside edges of the quilt.

Next we have a picture of the grain lines for the corner triangle cuts. These cuts also put the grain lines along the outside edges of the quilt.

For more information on grain lines, check out the Recommendations at the end of this article.

NOTE: Another way to cut side and corner triangles is to cut strips and use a specialty ruler. This method is covered in the article, Using Rulers to Cut Setting and Corner Triangles (coming soon).

How to Use the Triangle Cutting Chart

Step 1 – First, find the finished block size in column 1.

Step 2 – Next, find the corresponding number in column 2. Cut squares to this size in inches. One square gives you 4 side triangles.

Step 3 – Finally, find the corresponding number in column 3. Cut 2 squares to this size in inches. One square gives you 2 corner triangles.

NOTE: When in doubt about what size to cut, always round UP just to be sure. You can always trim it down later.

Finished Block Size
(Inches)
Side Triangles

  1. Cut squares in inches.
  2. Cut twice on diagonal.

Corner Triangles

  1. Cut 2 squares in inches.
  2. Cut once on diagonal.

3.0 5-1/2 3
3.5 6-1/4 3-5/8
4.0 7 3-3/4
4.5 7-5/8 4-1/8
5.0  8-3/8  4-1/2
5.5  9-1/8  4-7/8
6.0  9-3/4  5-1/8
6.5  10-1/2  5-1/2
7.0  11-1/4  5-5/8
7/5  12  6-1/4
8.0  12-5/8  6-5/8
8.5  13-3/8  6-7/8
9.0  14  7-1/4
9.5  14-3/4  7-5/8
10.0  15-1/2  8
10.5  16-1/8  8-3/8
11.0  16-7/8  8-3/4
11.5  17-1/2  9-1/8
12.0  18-1/4  9-3/8
12.5  19  9-3/4
13.0  19-3/4  10-1/8
13.5  20-3/8  10-1/2
14.0  21-1/8  10-7/8
14.5  21-3/4  11-1/8
15.0  22-1/2  11-1/2
15.5  23-1/4  12
16.0  24  12-1/4
16.5  24-5/8  12-5/8
17.0  25-3/8  13
17.5  26-1/8  13-1/4
18.0  26-3/4  13-5/8

Triangle Math

If you prefer to do the math yourself, here are the formulas:

Side Triangles

(Finished block size in inches x 1.414) + 1.25″

Corner Triangles

(Finished block size in inches / 1.414) + .875″


Recommendations

square ruler for triangle cutting chart

9-1/2″ Square Ruler

square ruler for triangle cutting chart

12-1/2″ Square Ruler

square ruler for triangle cutting chart

16-1/2″ Square Ruler

ArticleGrain Lines in Quilting

Article Quilt Blocks Set On-Point

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2 thoughts on “Side Triangle and Corner Triangle Cutting Chart

  1. Look at the size square you have to cut for a side triangle for a finished 10″ block. I don’t think a 5 1/2″ block will work for side triangles. The size for the 9.5 block is 14 3/4″.

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