📏 Enter known values
Formula Reference
Calculate the Perimeter
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And leave empty
Calculate the Side_A
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And leave empty
Calculate the Side_B
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And leave empty
Calculate the Side_C
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And leave empty
Perimeter of a Triangle
The perimeter of a triangle calculator finds any of these four values: Perimeter, Side A, Side B or Side C. The perimeter is the total length around the triangle, so it works for any type of triangle: equilateral, isosceles, scalene or right. Enter three values and the missing one is calculated automatically.
How it works
The perimeter is the sum of the three sides:
\[ Perimeter = Side_A + Side_B + Side_C \]
To find a missing side, subtract the other two sides from the perimeter. For the triangle to exist, each side must be shorter than the sum of the other two.
Example
A triangle has sides of 6, 5 and 4. The perimeter is 6 + 5 + 4 = 15. If you know the perimeter is 15 and two sides are 6 and 5, leave the third side empty and the calculator finds 4.
External Resources
- Types of triangles and how to find the perimeter by adding the sides — Math is Fun
- Triangle definition, properties, and perimeter — Wikipedia
- The triangle inequality: when three lengths form a triangle — Wolfram MathWorld