## Calculating the section modulus

To calculate the section modulus, the following formula applies:

where I = moment of inertia, y = distance from centroid to top or bottom edge of the rectangle

For symmetrical sections the value of **Z** is the same above or below the centroid.

For asymmetrical sections, two values are found: **Z** max and **Z** min.

To calculate the value of **Z** for a simple symmetrical shape such as a rectangle:

where

and y =

This gives the formula for **Z** as:

Note: The standard form of writing the value of **Z** is to write it as a number x 10^{3} mm^{3}, eg a value of 2,086 is written as 2.086 x 10^{3}.