HOW DO I?

Figure the size of HST (Half Square Triangles) needed to make Square-in-a-Square blocks with a uniquely sized center square


Triangle Calculators will figure the dimensions for the corner triangles needed for any size center square to make a Square-in-a-Square block.
While this example shows how to use the Triangle Designer to make HST, the Triangle calculators can be very helpful when figuring measurements for “funky” triangles cut from rectangles. ​

1


Determine the finished size of the center square

This square measures 6 1/2, which is its CUT size. Therefore, consider the seam allowance (1/4" each side) and subtract it (1/2" ) from the overall size (6 1/2") to find the FINISHED size of 6".
If you prefer to work with cut size when using the Yardage Calculator make this small adjustment.


2



Open Triangle Calculators in Notions — HALF SQUARE & CORNER
Choose half square triangles for this project to put the straight of grain on the outside of the block.
Quarter square triangles have stretchy, bias edges on the outside of the block. In contrast, Half square triangles avoid stretching because they place the straight grain on the outer edges. Learn more about the significance of fabric grain as you plan projects.

The calculator determines the size of the square you need to get your half square triangles. Follow these steps:
  1. Set switch to Corner. This gives you control over the length of the diagonal on the triangle.
  2. Enter block size in Finished Block On Point Size. Enter finished size of the center square, in this example that is 6".
  3. Adjust Seam to the seam allowance.

In this example, the calculator figures that we need to cut a 5 1/8" square.
What will be the block's finished size?

Two half square triangles will make one side of the block. So double the finished size of the triangle (4 1/4") to determine the block will have a FINISHED size of 8 1/2".


3



Figure yardage for triangles
Use the Yardage Calculator to figure the fabric needed for the Corner Triangle with a 4 1/4" finished size (or set the seam allowance to 0" and enter the cut size of 5 1/8") and the number of triangles needed (not the number of squares to cut!)

The QuiltSandwich app figures yardage and shows in a cutting diagram how to cut the number of strips to subcut into squares and then subcut into triangles.
Quick Calc is set at quarter-inch increments, just tap ‘Switch Calc’ in the upper left of the Yardage Calculator to go to Super Calc where any measurement and changes to allowances can be input.
A good resource to find decimal values for fractions is Conversions in Notions. It has tables with decimal values for many unusual fractions like 1/8" (which is .125)


4



Cut squares to size, then into half triangles

Create the half square triangles using the CUT size for your square.

In this example, the CUT size is a 5 1/8" square.


5



Assemble the Square-in-a-Square block

After assembly we can check the block size.

In this example, the assembled block CUT size is 9" square with a FINISHED size of 8 1/2".

Exactly as calculated by the Half Square Triangle Calculator!