Formula

Perimeter of a Triangle

The perimeter of a figure is the total length of its boundary. For a triangle with sides of lengths aa, bb, and cc, the perimeter is the sum of all three side lengths:

P=a+b+cP = a + b + c

To find a triangle's perimeter, add together the lengths of its three sides. If the perimeter and two side lengths are known, the third side can be found by subtracting the two known sides from PP.

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Updated 2026-04-21

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