Can this calculator handle irregular decagons with unequal sides?

The calculator provides formulas for area (≈7.694 × side²), perimeter (10 × side), and radii, which are displayed alongside a short article explaining each derivation.

How many diagonals does a regular decagon have?

A regular decagon has 35 diagonals; the calculator lists the lengths of diagonals across 2, 3, 4, and 5 sides based on the entered side length.

What is the formula for the area of a regular decagon?

Area = 2.5 × side² × √(5 + 2 × √5), which approximates to 7.694 × side².

Does the tool show the interior and exterior angles?

Yes, the results include both the interior angle (144°) and the exterior angle (36°) for a regular decagon.

Geometry & ShapesFree Tool

Decagon Calculator

Provided byOmni Calculatoromnicalculator.com

Decagon calculator will teach you all there is about regular polygons with ten sides and ten angles!

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Screenshot of Decagon Calculator on Omni Calculator — omnicalculator.comOpen the live tool →

About this tool

What Decagon Calculator does

A regular decagon calculator designed to compute all key geometric properties of ten-sided polygons. Users input a single known value—typically side length—and instantly receive outputs for perimeter, area, circumcircle radius, incircle radius (apothem), interior and exterior angles, and the lengths of five distinct diagonal types. The result is presented alongside a concise article that explains the underlying formulas and answers common decagon questions, turning the calculator into a quick reference for students and professionals alike.

Step by step

How to use the Omni Calculator Decagon Calculator

1
Open the Decagon Calculator on Omni Calculator and locate the Side (a) input field.
2
Enter the known side length value to generate all other measurements.
3
Review the automatically calculated Perimeter, Area, Circumcircle radius (R), and Incircle radius / apothem (r).
4
Scroll through the results to find the five diagonal lengths (across 2, 3, 4, and 5 sides) and angle measures.
5
Use the Share result or Clear all buttons to export or reset the calculation as needed.

Is it right for you

Best for

Students, educators, and designers who need fast, accurate decagon measurements without manual formula lookups or geometry software.

Limitations

Calculations apply only to regular decagons with equal sides and angles.
Requires at least one known input value; cannot generate properties from zero or irregular inputs.
Outputs are estimates based on standard geometric formulas and may not account for specific architectural scaling needs.

Questions

Decagon Calculator FAQ

Can this calculator handle irregular decagons with unequal sides?: The calculator provides formulas for area (≈7.694 × side²), perimeter (10 × side), and radii, which are displayed alongside a short article explaining each derivation.
How many diagonals does a regular decagon have?: A regular decagon has 35 diagonals; the calculator lists the lengths of diagonals across 2, 3, 4, and 5 sides based on the entered side length.
What is the formula for the area of a regular decagon?: Area = 2.5 × side² × √(5 + 2 × √5), which approximates to 7.694 × side².
Does the tool show the interior and exterior angles?: Yes, the results include both the interior angle (144°) and the exterior angle (36°) for a regular decagon.

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