A **half square triangle (HST) calculator** is an essential tool for **quilters **and **fabric crafters** using **Finished size + 7/8 inch = Size of squares to cut** formula.

It helps determine the size of **fabric squares** needed to create **half square triangles**, which are fundamental building blocks in many **quilt designs**.

The **hst calculator** takes the guesswork out of **fabric cutting** by providing **precise measurements** for creating **HSTs** of various sizes.

This ensures accuracy in your quilting projects and reduces fabric waste.

**Sample conversions:**

- To create a 4-inch finished
**HST**:- Input: 4 inches (finished size)
- Output: Cut two 4 7/8-inch squares

- To create a 2.5-inch finished
**HST**:- Input: 2.5 inches (finished size)
- Output: Cut two 3 3/8-inch squares

## Half Square Triangle Calculator

Desired Finished Size | Calculation | Cut Square Size | Number of HSTs |
---|---|---|---|

3 inches | 3 + 7/8 = 3 7/8 | 3 7/8 inches | 2 |

4.5 inches | 4.5 + 7/8 = 5 3/8 | 5 3/8 inches | 2 |

2.25 inches | 2.25 + 7/8 = 3 1/8 | 3 1/8 inches | 2 |

6 inches | 6 + 7/8 = 6 7/8 | 6 7/8 inches | 2 |

3.75 inches | 3.75 + 7/8 = 4 5/8 | 4 5/8 inches | 2 |

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## Half Square Triangle Formula

The formula for calculating the size of squares needed to make **HSTs** is:

**Finished size + 7/8 inch = Size of squares to cut**

This formula adds 7/8 inch to the desired finished size of your **HST**.

The extra 7/8 inch accounts for the 1/4 inch seam allowance on each side and the fabric lost in the diagonal cut.

**Examples:**

- For a 6-inch finished
**HST**: 6 + 7/8 = 6 7/8 inches Cut two 6 7/8-inch squares - For a 3.5-inch finished
**HST**: 3.5 + 7/8 = 4 3/8 inches Cut two 4 3/8-inch squares

## How do you calculate **half square triangles**?

Calculating **half square triangles** involves several steps:

**Determine the finished size**of your desired**HST**.**Add 7/8 inch**to the finished size.**Cut two squares**of fabric to the calculated size.**Place squares right sides together**.**Draw a diagonal line**from corner to corner on the wrong side of one square.**Sew 1/4 inch away**from both sides of the drawn line.**Cut along the drawn line**to create two**HSTs**.**Press open and trim**to the desired size if necessary.

This method ensures accurate **HSTs** with proper seam allowances.

## What size squares make two **half square triangles**?

The size of squares needed depends on the desired finished size of your **HSTs**. Here’s a quick reference:

- For 2-inch finished
**HSTs**, cut 2 7/8-inch squares - For 3-inch finished
**HSTs**, cut 3 7/8-inch squares - For 4-inch finished
**HSTs**, cut 4 7/8-inch squares - For 5-inch finished
**HSTs**, cut 5 7/8-inch squares

Remember, these measurements create two **HSTs** from two squares. Always cut two squares of the calculated size to create a pair of **HSTs**.

## What size half square triangles do charm packs make?

Charm packs typically contain 5-inch square fabric pieces. To calculate the size of **HSTs** that can be made from charm packs:

**5 inches – 7/8 inch = 4 1/8 inches**

Charm packs can create **HSTs** with a **finished size of 4 1/8 inches**. Many quilters prefer to trim these down to 4 inches for easier math and more consistent results in quilt patterns.

## What is a triangle half of a square?

A triangle that is half of a square is literally one half of a square that has been cut diagonally from corner to corner. In quilting terms, this refers to a **Half Square Triangle (HST)**.

Key characteristics of an **HST**:

- It has one 90-degree angle and two 45-degree angles.
- The longest side (hypotenuse) forms the diagonal of the original square.
- When two
**HSTs**are sewn together along their longest sides, they reform a square.

## Half square triangles 4 at a time chart

Finished HST Size | Cut Square Size |
---|---|

2 inches | 5 1/4 inches |

2.5 inches | 6 1/4 inches |

3 inches | 7 1/4 inches |

3.5 inches | 8 1/4 inches |

4 inches | 9 1/4 inches |

To use this method:

- Cut two squares to the size indicated.
- Place right sides together.
- Draw two diagonal lines corner to corner, forming an X.
- Sew 1/4 inch away from both sides of both lines.
- Cut horizontally, vertically, and on both drawn lines.
- Press open to reveal four
**HSTs**.

## Half square triangle size chart

Finished HST Size | Cut Square Size |
---|---|

1.5 inches | 2 3/8 inches |

2 inches | 2 7/8 inches |

2.5 inches | 3 3/8 inches |

3 inches | 3 7/8 inches |

3.5 inches | 4 3/8 inches |

4 inches | 4 7/8 inches |

4.5 inches | 5 3/8 inches |

5 inches | 5 7/8 inches |