Triangle Calculator
Given any three sides or angles of a triangle (with at least one side), compute remaining sides, angles, area, and perimeter.
Inputs
Area
—
Perimeter
—
Angles (A, B, C)
—
Sides (a, b, c)
—
Triangle type
—
About Triangle Calculator
Law of cosines
c² = a² + b² - 2ab·cos(C). Use it to find a side when you know two sides and the included angle (SAS), or to find an angle from three sides (SSS).
Law of sines
a/sin(A) = b/sin(B) = c/sin(C). Use it when you have ASA or AAS. Beware the "ambiguous case" SSA, which can have 0, 1, or 2 valid triangles.
Heron\u2019s formula
Area = √(s(s-a)(s-b)(s-c)) where s = perimeter/2. Computes area from three sides without needing angles. Stable for most triangles; can lose precision on very thin ones.