DIY Cost Tools
Regular Polygon Calculator
MATH & GEOMETRY CALCULATOR
Find regular polygon perimeter, area, apothem, and interior angle.
Use the same length unit throughout. All fields are required. Only convex regular polygons are supported. Side count must be a whole number from 3 to 10,000.
How to use this calculator
Enter your dimensions and select Calculate. Length results use your input unit, areas use its square, and volumes use its cube. Retain measurement precision until the final answer.
Formula and explanation
Perimeter = ns; apothem = s/[2tan(π/n)]; area = ns²/[4tan(π/n)]; interior angle = (n−2)180/n
A regular polygon has equal sides and equal interior angles.
Worked example
For Number of sides = 6, Side length (units) = 4, results are Perimeter (units): 24; Area (square units): 41.569219; Apothem (units): 3.4641016; Interior angle (degrees): 120.
Important limitations
Only convex regular polygons are supported. Side count must be a whole number from 3 to 10,000.
Ideal geometry does not account for manufacturing tolerances or measurement uncertainty. This is a calculation aid, not a structural design or building-code approval. Absolute inputs must not exceed one trillion.
Frequently asked questions
Can I calculate an irregular polygon?
No; unequal sides or angles require more information.
What is an apothem?
The perpendicular distance from the center to a side.
Can I mix inches and centimeters?
Convert all lengths to one unit first. Mixed units produce incorrect results.
Why did my result disappear?
Blank, invalid, or out-of-range inputs clear the previous result and display an instruction.
Review notes
Reviewed October 1, 2026. Default results were checked against the displayed formulas. Script tests covered blank, negative, nonfinite, and excessive inputs. Results run locally in your browser.