Triangle Calculator

Calculate area and perimeter using base/height or all three sides.

Key Facts

• Area can use base × height or Heron's formula.
• Perimeter = sum of all sides.

Formulas

• Equilateral Triangle Area
  Area = (√3 / 4) × a² - a = side length. Special formula since all sides are equal.
• Equilateral Triangle Perimeter
  Perimeter = 3 × a - Sum of all three equal sides.
• Isosceles Triangle Area
  Area = 0.5 × b × √(a² − (b² / 4)) - a = equal sides, b = base. Uses height derived from Pythagoras theorem.
• Isosceles Triangle Perimeter
  Perimeter = 2 × a + b - Sum of two equal sides and the base.
• Scalene Triangle Area (Heron's formula)
  Area = √(s × (s − a) × (s − b) × (s − c)) - a, b, c = sides; s = (a + b + c)/2. Works when height is unknown.
• Scalene Triangle Perimeter
  Perimeter = a + b + c - Sum of all three sides.
• Right-angled Triangle Area
  Area = 0.5 × a × b - a = base perpendicular, b = other perpendicular. Standard formula for right-angled triangles.
• Right-angled Triangle Perimeter
  Perimeter = a + b + c - Sum of base, perpendicular side, and hypotenuse.
• Right-angled Triangle Pythagoras Theorem
  c² = a² + b² - c = hypotenuse, a and b = perpendicular sides.

FAQs