Find the distance around a polygon from its side lengths, or use a side count for a regular polygon.
A triangle with sides 3, 4, and 5 has perimeter 12 units. Perimeter is the sum of the boundary side lengths.
3 + 4 + 5 = 12 units.
Embed Perimeter Calculator
Copy this iframe code into a page that permits embeds.
How to Use the Perimeter Calculator
For an irregular polygon, list each boundary side in order or any order, separated by commas. For a regular polygon, switch input type and provide the number of sides and one side length. Use one unit for every length. The calculator adds the boundary lengths and shows the side count and average side.
What Perimeter Measures
Perimeter is the total distance around a closed two-dimensional shape. Add every side once. For a regular polygon, all sides are equal, so multiply one side length by the number of sides.
Regular polygon: P = n × s
Perimeter Examples
Triangle
Sides 3, 4, and 5 have perimeter 3 + 4 + 5 = 12 units.
Rectangle
Sides 8, 6, 8, and 6 total 28 units. The rectangle formula 2(8 + 6) gives the same answer.
Regular hexagon
Six equal sides of length 4 give perimeter 6 × 4 = 24 units.
Checking Whether the Polygon Can Close
A side cannot be as long as or longer than all the other sides combined. This tool checks that necessary condition for the listed side lengths. If the check fails, the lengths cannot form a nondegenerate polygon. Passing the check does not determine a unique shape or area; angles may still vary.
Perimeter Is Different from Area
Perimeter uses linear units, such as meters or feet. Area measures the enclosed surface in square units. Two shapes can have the same perimeter but different areas, so side lengths alone may not be enough to answer an area question.
Perimeter Calculator FAQs
How do I find the perimeter of an irregular shape?
Add the lengths of every boundary side.
What is the perimeter of a regular hexagon?
Six times one side length.
Can sides 1, 1, and 5 make a triangle?
No. The longest side is greater than the sum of the other two.
Editorial review
SolverCalc names Prof. Dr. Khalil Mudassar as its educational reviewer. The formulas and examples are documented in the references below.
Sources
Disclaimer
For educational use. Check your class or textbook convention when the problem defines a different range, sequence index, or notation.