Triangle Calculator

Calculate area, angles, heights, perimeter, inradius, and circumradius of any triangle from three sides.

Side a

Side b

Side c

Tab to move between fields

Area

17.32

Perimeter20

Triangle TypeScalene Acute

Angle A38.21°

Angle B60°

Angle C81.79°

Height from A6.93

Inradius1.73

Circumradius4.04

How to Use This Calculator

Enter all three side lengths (a, b, c) of your triangle; the sides must satisfy the triangle inequality (each side < sum of the other two).
Area is computed using Heron's formula: A = √(s(s−a)(s−b)(s−c)) where s = (a+b+c)/2, so no height is needed.
All three interior angles are derived from the law of cosines: cos(C) = (a²+b²−c²)/(2ab).
The triangle is automatically classified as equilateral, isosceles, scalene, right, acute, or obtuse.
Inradius (r = Area/s) and Circumradius (R = abc/(4×Area)) are also shown for advanced geometry.
Altitude (height from each vertex) is computed as h = 2×Area / base.

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Formula

A = √(s(s-a)(s-b)(s-c)) where s = (a+b+c)/2

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