Perimeter of a Triangle Calculator

Your details

Pick the combination of sides and angles you already know. The calculator finds the rest.
Length of the first side.
Length of the second side.
Length of the third side (SSS mode only).
PerimeterScalene
21m

Sum of all three side lengths

Semi-perimeter (s)10.5m
Side a5m
Side b7m
Side c9m
Unitm

Perimeter: 21.0000 m

  • The perimeter is 21.0000 m. Add this amount of material (fencing, trim, border tape) to enclose the triangle.
  • The semi-perimeter is 10.5000 m. Plug it into Heron's formula to get the area without needing any angle measurements.
  • All three sides were entered directly, so no trigonometry was needed.

Next stepUse the semi-perimeter in Heron's formula (Area = sqrt(s(s-a)(s-b)(s-c))) to find the triangle's area without needing the height.

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