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Open calculator →Triangle Perimeter Calculator
Use your own values after reviewing the examples below.
Triangle perimeter formula
P = a + b + c
Add the three side lengths. If the sides are 6, 8 and 10, the perimeter is 24.
Check whether the sides can form a triangle
The sum of any two sides must be greater than the third side. If that condition fails, the three lengths do not form a triangle.
Example
A triangle with sides 5, 7 and 9 has perimeter 21. Its semiperimeter is 10.5.
For a right triangle where a side is missing, use the Right Triangle Calculator.
Frequently asked questions
What is the formula for triangle perimeter?
Add the three side lengths: P = a + b + c.
How do I know if three sides form a triangle?
The sum of any two side lengths must be greater than the remaining side.
Is perimeter the same as area?
No. Perimeter measures distance around the triangle; area measures the space inside it.