There are 2 ways to find the area of an octagon. The first only needs the side length. The second also uses the apothem.
When you only know the length of one side, use this formula:
If you also know the apothem, you can use either of these equivalent expressions:
Both expressions are equivalent and give the same answer.
In a regular polygon like an octagon, the apothem is the shortest distance from the center to any side. The image below shows it clearly:
Click on any element to learn more.
