How to Make Easy Quarter-Square Triangle Units

Ohio Star Quilt Block Pattern
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Overview
  • Total Time: 2 hrs
  • Skill Level: Intermediate

Quarter square triangle units are square patchwork units that are made up of four equally-sized 90-degree triangles. The fabric's sturdy straight grain runs parallel to the longest side of each triangle, where it helps keep the outer edges of units from stretching as you work on a quilt.

Quarter square triangle units are used in the outer midpoints of each Ohio Star quilt block illustrated here. The traditional Card Trick quilt block is another popular quilt block that's made in part from quarter-square triangle units. The units can be assembled by sewing triangles together individually but quick piecing methods are easier, and usually more accurate.

Learn how to make easy quick pieced quarter-square triangle units without cutting and sewing individual triangles. In this tutorial, you will be using half-square triangle units as parents for the quarter-square triangle patchwork units.

Notes

Before trying this technique you should be familiar with making half square triangle units.

What You'll Need

Equipment / Tools

  • Marking pen or pencil
  • Quilting rulers
  • Rotary cutter and mat
  • Sewing machine, set up to stitch
  • Iron and ironing board

Materials

  • Cotton fabric scraps for practicing

Instructions

  1. Sizing

    Choose a finished size for your quarter-square triangle units or refer to the quilt pattern for the unit dimensions.

    • Finished block size + 1-1/4 inches.

    Cut two (contrasting) squares to match the calculated size. For your practice quarter square triangles, let's make 3 x 3 inch units.

    • 3 inches + 1-1/4 inches = 4-1/4 inches.

    Your contrasting squares should be cut to 4-1/4-by-4-1/4 inches.

  2. Make and Mark HSTs

    Use the quick pieced half-square triangle unit method to create two half-square triangle units.

    • Turn one half-square triangle unit to its wrong side. Using the marking pen and ruler, draw a diagonal line corner to corner, crossing the seam.
    • Placing right sides together, line up the two units with contrasting triangles facing each other (same fabrics aren't stacked on top of each other!), edges matching all around. The seams should nest.

    Secure the squares together with pins so the fabrics don't shift.

    Illustrated design of how to cut quarter-square triangle units.
    Janet Wickell
  3. Sew and Cut

    Sew a 1/4 inch seam on each side of the drawn diagonal line. If you don't have a quarter-inch presser foot, mark the lines before sewing. This is the same method used to create the parent units.

    Using the rotary cutter and mat, cut the squares apart on the diagonal line, press units open and trim away triangular nubs at the ends of the seam allowances.

    You'll have two quarter square triangle units that are 1/2 inch wider and taller than the finished size.

    Tip

    You can use any method to construct the parent half-square triangle units. Try the Magic 8 technique if you're sewing lots of identical triangles and creating the Hunter's Star. Alter cutting sizes if other methods are used.

    Nine Ohio Star quilt blocks in orange and maroon.
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Quarter-Square Triangle Unit Variations

Change the appearance of quarter-square triangle units by constructing them with varying combinations of parent squares. 

  • When quarter-square triangle units are made from identical half-square triangle parents, the resulting patchwork squares are identical and symmetrical.
  • Substitute a plain square for one of the parents to make units with two quarter-square patches in one-half of the square and a single triangle in the other half. The units are mirror images of each other.
  • Use two different half-square triangle parents to make the quarter-square triangle units. The units are mirror images of each other, but that doesn't usually matter if you're making a scrap quilt.

As you consider the patchwork you need, weigh the advantages of quick piecing versus sewing individual triangles. For example, if you were making small quarter-square triangle units, you might opt for the quick-pieced method simply because it eliminates the need to handle tiny triangles.

If some units don't fit your project, throw extra units into a patchwork bin and use them later in another project.

If you decide to assemble quarter-square units from individual triangles, remember that the fabric's straight grain should be parallel to each triangle's longest edge.

Illustrated design of how to configure triangles.
Janet Wickell