Perimeter of a Triangle
Sum of the three sides of a triangle.
Formula
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Example
A triangle with sides 3, 4, 5 has perimeter 3+4+5 = 12.
How it works
The perimeter of a triangle is the total distance around its outside edge. Since a triangle has exactly three sides, you find that total by adding the lengths of all three sides together: a + b + c. This works because perimeter always means the full boundary length of a shape, measured along each side.
When to use it
Use this formula whenever you need the outside distance around a triangular shape, such as in fencing, framing, or finding how much trim is needed. It also appears in geometry problems where the side lengths are known and the total boundary is required.
Worked example, step by step
A triangular garden has sides of 6 m, 8 m, and 10 m. P = a + b + c P = 6 + 8 + 10 P = 24 The perimeter of the triangle is 24 m.
Common mistakes to avoid
- Forgetting to add all three sides
- Using area formulas instead of perimeter
- Leaving the answer without the correct unit
Did You Know?
The triangle inequality guarantees any two sides must together exceed the third — or the triangle can't close.
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