Triangle Perimeter Calculator
Calculate the perimeter of any triangle
Enter Triangle Sides
Triangle Diagram
About Triangle Perimeter
The perimeter of a triangle is the total distance around the triangle, calculated by adding the lengths of all three sides together.
Perimeter Formula
For any triangle with sides a, b, and c: P = a + b + c
Triangle Inequality Theorem
For three sides to form a valid triangle, the sum of any two sides must be greater than the third side:
- a + b > c
- a + c > b
- b + c > a
Frequently Asked Questions
How do you find the perimeter of a triangle?
Simply add all three sides together: P = a + b + c. Make sure all sides are in the same units.
What is the triangle inequality theorem?
The triangle inequality states that the sum of any two sides must be greater than the third side. If this isn't true, the three sides cannot form a triangle.
Can I find perimeter if I only know two sides?
No, you need all three sides to calculate the perimeter. However, if you know two sides and an angle, you can first calculate the third side using the law of cosines.
What's the difference between perimeter and area?
Perimeter is the distance around the triangle (measured in linear units like cm or inches), while area is the space inside the triangle (measured in square units like cm² or square inches).
What is the semi-perimeter of a triangle?
The semi-perimeter is half the perimeter: s = P/2 = (a + b + c)/2. It's used in Heron's formula to calculate triangle area.
Does the type of triangle affect perimeter calculation?
No, the formula P = a + b + c works for all types of triangles: right, acute, obtuse, scalene, isosceles, and equilateral.
How do I convert perimeter units?
Convert each side to the desired unit first, then add them. Or calculate the perimeter and then convert. For example, if sides are in feet, the perimeter is in feet.
What's the perimeter of an equilateral triangle?
For an equilateral triangle where all sides equal s, the perimeter is simply P = 3s.