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Triangle Calculator

Sides, angles, area and perimeter from any 3 values

Enter any 3 values (at least 1 side). Use degrees for angles. Leave others blank.

Formulas used

  • Law of cosines: c² = a² + b² − 2ab·cos(C) — solve for any side given two sides and included angle
  • Law of sines: a/sin(A) = b/sin(B) = c/sin(C) — find missing sides or angles
  • Heron's formula: Area = √(s(s−a)(s−b)(s−c)) where s = (a+b+c)/2
  • Angle sum: A + B + C = 180°

Triangle types

  • Equilateral: all sides equal, all angles 60°
  • Isosceles: two sides equal
  • Scalene: all sides different
  • Right: one 90° angle (a² + b² = c²)
  • Acute: all angles < 90°
  • Obtuse: one angle > 90°