# How to Measure the Length of the Diagonal Line of a Square

The diagonal line of a square is the cross measurement. This is called the hypotenuse. You can measure the length of the diagonal line of a square with the Pythagorean Theorem. This calculation can be used for any square or rectangle shape which has right angles. You can even use it to measure the length of any right triangle. When you know the length of two legs, it is easy to calculate the hypotenuse or diagonal line.

#### Things You'll Need

• Measurements of the square
• Calculator (optional)

## Instructions

• 1

Measure the sides of the square. When you are building a pole barn or garage, you will want to know the dimensions of the building to determine the cross measurement. By calculating the cross measurement, you can be assured the building is going to be square.

• 2

Calculate the diagonal line of a square by using the measurements in the pythagorean theorem. The formula looks like this:

A^2+B^2=C^2 or A squared plus B squared equals C squared.

An example would be a square measures 15 by 15.

• 3

Add A squared to B squared. In this case it would be 15 squared plus 15 squared or 225 plus 225. The result would be 450.

• 4

Find the square root of the product. The product in this equation would be 450. The square root would be 21.21. Most calculators can calculate the square root of a number.

• 5

Use this formula any time you need to measure the length of the diagonal line of a square. You can also use this same formula to find the measurement of a right triangle. If you know the length of the two legs then you can find the measurement of the diagonal line between them, or the hypotenuse. For instance, if a triangle leg measures 7 inches, the hypotenuse would be 9.9 inches.

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