Perimeter of a Triangle Formula
Geometry Formulas: Area, Volume, Perimeter
What is the formula for the perimeter of a triangle?
Answer
Perimeter of a triangle
P = a + b + c
Here a is the side (or base), b is the second side, c is the third side. The result comes out in units.
Where the formula comes from
P = a + b + c
There is nothing to derive: the perimeter of any polygon is the sum of its sides, and a triangle has three. The height, which the area formula needs, plays no part here.
Worked examples
Let a = 3, b = 4, c = 5. Then the perimeter of a triangle = 12 units.
Let a = 6.5, b = 7, c = 4.2. Then the perimeter of a triangle = 17.7 units.
The common mistake
Adding three lengths that cannot make a triangle. Any two sides together must exceed the third — 2, 3 and 9 have a sum, but no triangle.
Other quantities: Triangle
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See Also
- Square Footage Calculator - Width × length in feet to square feet
- Square Feet to Square Meters (Sq Ft to Sq M) - Convert Square Feet to Square Meters
- Square Meters to Square Feet (Sq M to Sq Ft) - Convert Square Meters to Square Feet
- Gravel Calculator - Area to cubic yards, tons and coverage
- Topsoil Calculator - Cubic yards, weight and coverage for any area
- Multiplication Facts - Any two numbers from 1 to 9, with the working shown
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Values from the Formula (b = 4, c = 5)
| If a = | Perimeter |
|---|---|
| 2 | 11 units |
| 3 | 12 units |
| 4 | 13 units |
| 5 | 14 units |
| 6 | 15 units |
| 8 | 17 units |
Geometry Formulas: Area, Volume, Perimeter
These are the formulas for the area, perimeter, circumference, volume and surface area of the standard shapes — 31 of them. Each page shows not only the formula but where it comes from, what every letter stands for, two worked examples and the mistake that this particular shape invites. For example, it can help you find out what is the formula for the perimeter of a triangle? (The answer is: P = a + b + c). Pick the pair — "Area of a circle", for instance — and hit the "Find out" button.
Geometry Formulas: Area, Volume, Perimeter