## Half Square Triangle Calculator

This **half square triangle calculator** helps determine the **size of fabric squares** needed to create **half square triangles**, which are **fundamental components** in many quilt designs.

`HSTs are created by `**sewing two squares of fabric together diagonally** and then **cutting them apart** to form **two triangular units**.

You want to make a

4-inch finished HST, you would typically start withtwo 5-inch squares. Thehst calculatortakes into account theseam allowanceand the fact that you’re working with thediagonal of the square. By inputting your desiredfinished size, the calculator provides theinitial square size needed, saving time and reducingfabric waste.

## Half Square Triangle 4 Time 2 Time Size Chart

Finished HST Size | 4x Starting Square Size | 2x Starting Square Size |
---|---|---|

1 inch | 4 inches | 2 inches |

2 inches | 8 inches | 4 inches |

3 inches | 12 inches | 6 inches |

4 inches | 16 inches | 8 inches |

5 inches | 20 inches | 10 inches |

## Half Square Triangle Formula

The formula for calculating the **starting square size** for a **Half Square Triangle** is:

**Finished HST size + 7/8 inch = Starting square size**

A **finished HST of 3 inches**: **3 inches + 7/8 inch = 3 7/8 inches**

This formula accounts for the

1/4 inch seam allowanceand thediagonal cut. The extra7/8 inchensures that your HST will be thecorrect size after trimming.

## What is a triangle half of a square?

A **triangle half of a square** is literally what it sounds like – a **triangle that forms half of a square** when two of them are placed together. In quilting terms, this refers to a **Half Square Triangle (HST)**.

You take a

5-inch squareand cut itdiagonally from corner to corner, you’ll end up withtwo triangles. Each of these triangles ishalf of the original square. When these triangles aresewn together along their long edges(thehypotenuse), they form anew squarethat’s slightly smaller than the original due toseam allowances.

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