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Triangle Perimeter calculadora

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Perimeter
12
P = a + b + c

Add the three sides of any triangle to get the perimeter. Supports scalene, isosceles and equilateral, with shortcut formulas and a worked example.

Written by Laura WhitmoreReviewed by Editorial Desk

How it works

What perimeter means for triangles

The triangle perimeter calculadora on this page is built around one idea: walk once around the edge and add every straight segment. Unlike area, perimeter never cares about angles — only lengths. That is why you can find the perimeter of a scalene triangle without knowing any angles, as long as you have all three sides.

Three worked examples

Scalene — sides 7 cm, 10 cm, 12 cm

P = 7 + 10 + 12 = 29 cm. No special formula — just addition.

Equilateral — side 4.5 m

P = 3 × 4.5 = 13.5 m. Fencing a triangular flower bed with equal sides? Order 14 m of edging and allow 5% overlap.

Isosceles — equal sides 8 inches, base 6 inches

P = 2 × 8 + 6 = 22 inches. Convert to cm for a UK supplier: 22 × 2.54 ≈ 55.9 cm using our **length converter**.

When you only know two sides

If the triangle is right-angled and you know two sides, use the **Pythagoras calculadora** to find the third, then add. If you know SAS (two sides and the included angle), use the cosine rule to find the third side first.

  • Right triangle — missing side from **Pythagoras or hypotenuse** tool.
  • Any triangle — third side from cosine rule, then P = a + b + c.

Works well with

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Frequently asked questions

What is the formula for triangle perimeter?
P = a + b + c, the sum of the three side lengths.
How do you find the perimeter of an equilateral triangle?
P = 3s where s is the length of one side.
Can you find perimeter from area?
Not uniquely — many different triangles can share the same area but have different perimeters. You need side lengths or enough information to derive them.
What units should I use?
Any length unit, but all three sides must be converted to the same unit before adding.
What if I only know the base and height?
That fixes area, not perimeter. You need at least one more constraint (an angle, another side, or that it is isosceles/right) to pin down the sides.
Does a triangle’s perimeter change if I rotate it?
No — perimeter is a length, independent of orientation.
How is this different from circumference?
Circumference refers to circles. For triangles we say perimeter.
What is Heron’s formula used for?
Area from three sides — not perimeter. Once you have the sides, perimeter is still just a + b + c.
Can perimeter be a decimal?
Yes — sides are often decimals in real measurements.
Is the perimeter the same as the boundary length?
Yes — in polygon terminology they mean the same thing.

References

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