Area Calculator

  • Decagon Area Calculator
    Calculate the area of a regular decagon (10-sided polygon) from its side length using the exact formula Area = (5/2)·s²/tan(π/10).
  • Circumference and Area of a Circle Calculator
    Calculate the circumference and area of a circle from its radius. Uses C = 2πr and A = πr². Instant results with diameter and worked formulas.
  • Square in a Circle Calculator
    Find the largest square that fits inside a circle. Enter the radius to get the inscribed square's side, diagonal, area, perimeter and fill ratio.
  • Semicircle Area Calculator
    Calculate the area and perimeter of a semicircle from its radius. Free online tool using A = πr²/2 with instant area, arc length and perimeter.
  • Quadrilateral Area Calculator
    Calculate the area of a quadrilateral with precision using the Quadrilateral Area Calculator. Input four side lengths to determine the shape's area easily and accurately.
  • Heron's Formula Calculator
    Calculate the area of any triangle from its three side lengths using Heron's formula. Instantly get the area, semi-perimeter, and perimeter.
  • Star Shape Calculator
    Calculate the area, edge length and perimeter of an n-pointed star polygon from its outer radius R and inner radius r. Free, instant, and accurate.
  • Circular Segment Area Calculator
    Calculate the area of a circular segment from radius and central angle (degrees or radians). Also returns arc length, chord length, and sagitta height.
  • Regular Polygon Calculator
    Calculate the area, perimeter, interior & exterior angles, apothem and circumradius of any regular polygon from its number of sides and side length.
  • Pentagon Calculator
    Calculate the area, perimeter, apothem, circumradius and diagonal of a regular pentagon from its side length with exact geometric formulas.
  • Octagon Calculator
    Calculate the area, perimeter, apothem, circumradius and diagonal of a regular octagon from its side length using exact geometric formulas.
  • Hexagon Calculator
    Calculate the area, perimeter, apothem and diagonal of a regular hexagon from its side length. Free, instant, with formulas and worked examples.
  • Ellipse Calculator
    Calculate the area, perimeter (Ramanujan approximation), eccentricity and focal distance of an ellipse from its semi-major and semi-minor axes.
  • Cross-Sectional Area Calculator
    Calculate the cross-sectional area of a circle (A=πr²), rectangle (A=w·h), or pipe/annulus (A=π(r_out²−r_in²)) instantly with this free tool.
  • Quadrilateral Area from Four Sides and Opposite Angles (Bretschneider's Formula)
    Compute the area and perimeter of any quadrilateral from its four side lengths and the sum of one pair of opposite angles using Bretschneider's formula.
  • Cyclic Quadrilateral Area Calculator
    Compute the area and perimeter of a cyclic quadrilateral from its four side lengths using Brahmagupta's formula. Free, instant, with validity check.
  • Area of an Obtuse Triangle Calculator
    Find the area of an obtuse triangle using base and height or Heron's formula from three sides. Free, instant, and accurate online calculator.
  • Irregular Polygon Area Calculator
    Find the area of any irregular polygon from its vertex coordinates using the Shoelace formula. Also returns perimeter and vertex count. Free and instant.
  • Basal Area Calculator
    Calculate tree basal area from DBH in inches using the forestry constant 0.005454 × DBH². Get per-tree and total stand basal area in square feet.
  • Annulus Area & Circumference Calculator
    Calculate the area, circumference, width and diameters of an annulus (flat ring) from any two dimensions: outer/inner radius, width, or diameters.
  • Annulus Calculator
    Annulus calculator: enter any two of the outer/inner radius, circumference or area and solve all ring properties — radii, circumferences, areas and annulus area.
  • Area Between Two Curves Calculator
    Compute the area between two curves f(x) and g(x) over an interval [a,b] using definite integration of |f−g|. Handles crossings automatically.
  • Rabbit Cage Size Calculator
    Calculate the minimum cage area and recommended floor space your rabbit needs based on its stretched length, width, and the number of rabbits housed.
  • Area of a Circle Calculator
    Calculate the area of a circle instantly from its radius or diameter using A = πr². Also returns diameter and circumference. Free online geometry tool.

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