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Pentagon Calculator.

Calculate regular pentagon area, perimeter, and apothem from its side length.

On-device calculationNo signup
01

Set your values

Results update as you type.

area: 43.011935

area

43.011935
perimeter: 25

perimeter

25.000000
apothem: 3.440955

apothem

3.440955

Results update automatically as you type.

Use Cases

Geometry homework and math practice

Students can quickly verify their manual calculations for area, perimeter, and apothem of a regular pentagon, helping them understand the relationships between these measurements.

Example: Given a side length of 5 units, find the area and perimeter.

Design and construction planning

Architects, designers, and DIY enthusiasts can use the calculator to determine the space a pentagonal element will occupy, such as a tabletop or a garden bed, by inputting the side length.

Example: A pentagonal tile with side length 2 feet: what is its area?

Frequently Asked Questions

What is a regular pentagon?
A regular pentagon is a five-sided polygon where all sides are equal in length and all interior angles are equal (108 degrees). This calculator uses the side length to compute its geometric properties.
How is the apothem calculated?
The apothem is the distance from the center to the midpoint of a side. For a regular pentagon with side length 's', the apothem is calculated as s / (2 * tan(π/5)). This calculator uses that formula.
Can I use this calculator for irregular pentagons?
No, this calculator is specifically for regular pentagons, where all sides and angles are equal. For irregular pentagons, you would need different formulas and more information.

Tips & Common Mistakes

Tips

  • Ensure the side length is positive; the calculator assumes a valid regular pentagon.
  • Use consistent units for side length to get area in square units and perimeter in the same unit.
  • The apothem is useful for finding the area using the formula: Area = (perimeter * apothem) / 2.
  • For quick estimates, remember that the area of a regular pentagon is approximately 1.72 times the square of the side length.

Common Mistakes to Avoid

  • Using the diameter or diagonal instead of the side length; the calculator only accepts the side length.
  • Forgetting to convert all measurements to the same unit before calculating, which can lead to incorrect results.
  • Assuming the apothem is the same as the radius; the apothem is the distance to a side, not to a vertex.

Last updated: August 13, 2026