Half square triangle unit

Half Square Triangle

2 - 3 inch units from 44 inch fabric bolt width

There are several methods to make half square triangles. Following are instructions to make 2 half square triangle units from 2 fabric squares. To calculate how large to cut squares, add 7/8 inch seam allowance to what you want finished unit size to be. Below calculations are made using this formula.


Unit size
Number of units
Fabric bolt width


Fabric 1
Cut 1 - 37/8 inch square.
Fabric 2
Cut 1 - 37/8 inch square.


Figure 1
  • Match 1 square of each fabric right sides together.
  • Draw a diagonal line from corner to corner on wrong side of lighter fabric.
  • Sew 1/4 inch seam on both side of diagonal line.
  • Cut units apart on drawn diagonal line.
  • Press seam to one side.
  • Makes 2 half square triangle units.

Tip: Put desired fabrics right sides together and then cut squares. This way, square pairs will already be matched.