Triangle Perimeter Calculator
Find the perimeter of a triangle by summing all three side lengths.
Inputs
units
units
units
Perimeter
21.0000units
Step by step
Sum all sides
P = 5 + 7 + 9
= 21
How it works
The perimeter of a triangle is simply the sum of all three side lengths.
Formula
Triangle Perimeter
P = a + b + c
- a
- First side
- b
- Second side
- c
- Third side
Frequently Asked Questions
Do the sides need to satisfy the triangle inequality?
Yes — any two sides must sum to more than the third for a valid triangle, but this calculator sums them regardless.
Is perimeter the same as circumference?
Circumference typically refers to circles. For polygons (including triangles), we use the term perimeter.