Math
Polygon Interior Angle Calculator
Use this polygon angle calculator for regular polygons and classroom geometry angle-sum problems.
Try an example
Result
Each regular interior angle
—
- Interior angle sum
- —
- Each exterior angle
- —
Student quick launch
Grade planning, algebra checks, and formulas students reach for most.
Study path
Use this calculator with
Follow these when you want the formula behind the answer, a short lesson, or nearby tools in the same topic.
What the polygon interior angle calculator solves
Use this polygon angle calculator for regular polygons and classroom geometry angle-sum problems.
Formula
How to use it
- Enter the number of sides.
- Use the sum for any simple polygon.
- Use the per-angle value only when the polygon is regular.
How to read the answer
A regular polygon has equal sides and equal interior angles.
Common mistakes and edge cases
- The per-angle result assumes a regular polygon.
- A polygon needs at least 3 sides.
- Exterior angles around a convex polygon sum to 360 degrees.
Worked examples
Octagon
Each regular interior angle
135 deg
Triangle
Each regular interior angle
60 deg
Frequently asked questions
Does the angle sum require a regular polygon?+
No. The sum works for any simple polygon with n sides.
Why is each exterior angle 360/n?+
The exterior turns around a convex polygon add to one full turn, or 360 degrees.
About this calculator
- Written by
- mathcheck editorial team
- Last reviewed
- May 15, 2026
Method
- Uses the values entered by the user and stable formulas documented on the page.
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Last updated: May 15, 2026