Octagon Table: Area by Side length
Reference table of area for Octagon across a range of side length values — exact, engine-computed figures you can read off at a glance.
Octagon Calculator
Verified formula Updated Jun 2026 Private — runs on your device
Verified formula
Private
Area
120.7107
- Perimeter
- 40.0000
For general information only — not financial, tax, legal or medical advice. Verify before you rely on it.
How to use the Octagon Calculator
The Octagon Calculator works out your area, along with 1 related figure in an instant. Enter side length and the result updates as you type — it is free, needs no sign-up, and runs entirely in your browser so your figures stay private.
- Enter the side length.
- Read off your area, together with perimeter — the calculator updates automatically, with no button to press.
Formula
The Octagon Calculator uses the formula:
Area = 2 × (1 + √(2)) × Side length ^ 2
Worked example
For example, with side length of 5 units, the area is 120.7107.
| Side length | 5 units |
|---|
| Area | 120.7107 |
|---|---|
| Perimeter | 40.0000 |
Results are estimates for educational use, not professional advice.
Key terms explained
- Perimeter
- The total distance around the outside of a two-dimensional shape.
- Area
- The amount of two-dimensional space a shape covers, measured in square units.
Frequently asked questions
Use A = 2 × (1 + √2) × side², about 4.8284 × side². A side of 5 gives an area of about 120.71 square units.
A regular octagon has eight equal sides, so the perimeter is 8 × side. For a 5-unit side it is 40 units.
Yes. The formula needs all eight sides and angles equal. Irregular octagons must be split into simpler shapes.
Stop signs are the most familiar regular octagon, along with tiles, gazebos and some table and umbrella shapes.
The Octagon Calculator uses the formula: Area = 2 × (1 + √(2)) × Side length ^ 2. For example, with side length of 5 units, the area is 120.7107.
Enter the side length. Read off your area, together with perimeter — the calculator updates automatically, with no button to press.
Related guides
How to Calculate Octagon: Formula, Steps & Examples
Learn how to calculate Octagon — the formula explained step by step, with worked examples and a free calculator to check your answer.