Triangle Perimeter Calculator
Find the perimeter of a triangle by summing all three side lengths.
About Triangle Perimeter Calculator
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
Worked example
With the default values below, Triangle Perimeter Calculator returns Perimeter of 21.0000. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Side aminimum 0 units
- 5 units
- Side bminimum 0 units
- 7 units
- Side cminimum 0 units
- 9 units
Results
- Perimeter
- 21.0000 units
Step by step
- 1Sum all sides= 21
Assumptions and limits
- The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
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.