Cutting triangles and diamonds with a basic quilting ruler

cutting a strip of fabric with a rotary cutter and ruler with title.

Once you have strips cut with your basic quilting ruler, you often want to cut them down into other shapes. Many specialty rulers exist for triangles, but once you know how to use all the lines on your basic ruler, you can use it to cut not only square and rectangles, but also different styles of triangles and even diamonds.

Any of these shapes can be joined for great scrappy quilts.

Half Square Triangles

Half square triangles are triangles that are made by cutting squares on the diagonal from corner to corner. Two right angle triangles are made from a square and the long edge of the triangle (hypotenuse) is cut on the bias.

These can be cut from a strip of fabric by aligning the edge of the strip with the 45º line on the ruler.

cutting a right angle triangle with a basic quilting ruler and rotary cutter. Floral fabric and pink cutting mat.

Slide the ruler along the strip until the upper edge of the ruler lines up with the end of the strip. This will give you a half square triangle.

Quarter Square Triangles

It is important to know what kind of triangle you are working with. Quarter square triangles look the same as half square triangles, but the difference is which sides are cut on the bias.

Quarter square triangles (as you can probably guess from the name) would be made by cutting a square on both diagonals, leaving you with four identical squares. In this situation, the two short sides of the triangle are cut on the bias.

To cut a quarter square triangle from a strip of fabric, first cut the end of the strip on the 45º line as if cutting a half square triangle.

cutting a triangle from a strip of fabric with a rotary cutter and ruler.

Then turn the ruler and align the 45º line on the upper edge of the strip. Line up the edge of the ruler, so it will form the point of the triangle on the lower edge of the strip.

quarter square triangle cut of floral fabric with sides labelled.

This method is sometimes useful if you want right angle triangles, but your fabric is not wide enough to get half square triangles.

Equilateral Triangles

Equilateral triangles are triangles that have three equal sides. To cut these, you will use the 60º line on the ruler.

Begin by aligning the 60º line with the bottom of the strip and cutting off the end of the strip.

cutting a strip of fabric on a 60* angle.

Then turn the ruler to align the 60º line with the top of the strip.

second cut for an equilateral triangle from a strip of fabric.

This makes a perfect equilateral triangle. These are often used in scrappy quilts, or you can join six of them to make a hexagon.

equilateral triangle cut of floral fabric on a pink cutting mat.

Diamonds (aka parallelograms)

Once you know how to cut triangles, diamonds are easy.

Cut the edge of the strip with an angle just as if you were going to cut a triangle. Either 45º or 60º will work depending on how “flat” you want your diamond. 60º will be more tall and thin and 45º will be more square.

Once the first cut is made, align the ruler so that the straight lines are lined up with the cut edge. The cutting line will be parallel to the first cutting line.

cutting a parallelogram from floral fabric.

If you want to make a scrappy quilt with just one shape, it doesn’t really matter what size that shape is as long as they are all the same.

floral fabric diamond on pink cutting mat.

The reason why many people prefer specialized rulers is because it makes the math simple for cutting specific sizes. But if you are willing to experiment with scrap fabric, you can figure out what size shapes you need to cut and use the money on something else instead of a ruler. The choice is yours.

Either way, these shapes make great quilts.


Elizabeth DeCroos - Epida Studio.

Elizabeth DeCroos

Elizabeth DeCroos is the designer and teacher at Epida Studio. She loves to work in quilting, pojagi and embroidery and teach these techniques to others.
Learn more and get her to speak to your group.

Scroll to Top