Geometry Calculator

About This Tool

The Geometry Calculator instantly computes the area, perimeter, and other measurements for eight shapes: circle, rectangle, triangle, square, trapezoid, parallelogram, ellipse, and circle sector.

Triangles are calculated using Heron's formula from three side lengths — no height required. Sector angles are entered in degrees and converted to radians internally.

How to Use

1. Select the shape you want to calculate.
2. Enter the required dimensions (radius, side lengths, height, etc.).
3. Area and perimeter are calculated instantly.
4. Additional info (diagonal, diameter, arc length) is shown where applicable.

Formulas

• Circle: Area = πr², Circumference = 2πr
• Rectangle: Area = a × b, Perimeter = 2(a + b)
• Triangle: Area via Heron's formula √(s(s-a)(s-b)(s-c))
• Square: Area = a², Perimeter = 4a
• Trapezoid: Area = (a + b) / 2 × h
• Parallelogram: Area = base × height
• Ellipse: Area = πab, Perimeter ≈ 2π√((a²+b²)/2)
• Sector: Area = ½r²θ (θ in radians)

FAQ

• Why does the triangle need all three sides? — Heron's formula computes area from three side lengths alone — no height needed.
• How do I calculate a right triangle? — Enter all three side lengths. Use the Pythagorean theorem to find the hypotenuse if you only know two sides.