HOW DO I?
Figure yardage for any size HST (Half Square Triangle) or HalfRectangle
Use the Triangle Calculators in QuiltSandwich app to figure the dimensions for any size triangle. Then, enter the dimensions into QuiltSandwich's Yardage Calculator to find yardage and see a cutting diagram.
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Maybe you'll get the finished size from your design. Or, it might be you'll measure your workinprogress for cut size. Either works because the Triangle Calculators will report both dimensions.
The Yardage Calculator defaults to use finished sizes. However, if you prefer working in cut sizes or in a special situation find you must work with cut size, set the seam allowance in the Yardage Calculator to 0" adjust.
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This example will show the steps for a Corner Triangle.
Of quilters need to carefully choose which triangle to use for a project. 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 helps determine the size of the square you need to get your half square triangles. For this example:
In this example, the calculator figures that we need to cut a 5 1/8" square. What will be the block's finished size? 
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The Triangle Calculators have figured exactly the dimension need to calculate yardage. Enter into the Yardage Calculator:
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 quarterinch 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) 