- Volume Calculator
- Area Calculator
- Perimeter Calculator
- Surface Area Calculator
- Circle Calculator
- Rectangle Calculator
- Triangle Calculator
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Circumference of a Cylinder CalculatorCalculate the circumference of a cylinder from its radius or diameter using C = 2πr = πd. Fast, free, and accurate online geometry tool.
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Center of a Circle CalculatorFind the center (h, k) and radius of a circle from its general equation x² + y² + Dx + Ey + F = 0. Free, instant, step-by-step.
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Circumference and Area of a Circle CalculatorCalculate the circumference and area of a circle from its radius. Uses C = 2πr and A = πr². Instant results with diameter and worked formulas.
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String Girdling Earth CalculatorSolve the classic string-around-the-Earth puzzle. Add length to a string circling any sphere and find how high it lifts off the surface: h = ΔC/(2π).
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Square in a Circle CalculatorFind the largest square that fits inside a circle. Enter the radius to get the inscribed square's side, diagonal, area, perimeter and fill ratio.
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Equation of a Circle CalculatorFind the equation of a circle from its center (h, k) and radius r. Get the standard form, general form, diameter, circumference, and area instantly.
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Semicircle Area CalculatorCalculate the area and perimeter of a semicircle from its radius. Free online tool using A = πr²/2 with instant area, arc length and perimeter.
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Circumference CalculatorCalculate the circumference of a circle from its radius or diameter using C = 2πr = πd. Also returns the area, radius, and diameter instantly.
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Circumference-to-Radius CalculatorFind the radius of a circle from its circumference using r = C/(2π). Also returns diameter and area instantly. Free online geometry calculator.
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Circumscribed Circle CalculatorFind the circumradius of a triangle from its three sides. Computes R = abc/(4·Area) using Heron's formula, plus diameter, circumference and circle area.
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Circular Segment Area CalculatorCalculate the area of a circular segment from radius and central angle (degrees or radians). Also returns arc length, chord length, and sagitta height.
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Central Angle CalculatorFind the central angle of a circle from arc length and radius. Get the angle instantly in both radians and degrees with this free calculator.
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Chord Length CalculatorCalculate the chord length of a circle from its radius and central angle using c = 2r·sin(θ/2). Fast, accurate, with worked examples.
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Circumscribed Circle of a Regular Polygon CalculatorCompute the circumradius, circumscribed circle area, and polygon area of a regular n-gon from its side length, across a range of side counts n.
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Incircle of a Regular Polygon CalculatorCompute the inscribed circle (incircle) radius, incircle area and polygon area of a regular polygon from its side length, across a range of side counts n.
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Annulus Area & Circumference CalculatorCalculate the area, circumference, width and diameters of an annulus (flat ring) from any two dimensions: outer/inner radius, width, or diameters.
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Annulus CalculatorAnnulus calculator: enter any two of the outer/inner radius, circumference or area and solve all ring properties — radii, circumferences, areas and annulus area.
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Aperture Area CalculatorCalculate the area of a circular aperture from its diameter using A = π(D/2)². Get instant results in mm² and cm² for lenses, pipes, and openings.
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Arc Length CalculatorCalculate the arc length of a circle from its radius and central angle in degrees or radians. Also shows chord length and circumference.
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Sector Area Calculator (Degrees)Calculate the area of a circle sector from the radius and central angle in degrees. Free, instant, with arc length too. Formula A = (θ/360)·π·r².
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Area of a Circle CalculatorCalculate 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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Sector Area from Arc Length CalculatorCalculate the area of a circular sector from its radius and arc length using A = ½ · r · s. Fast, accurate, and free online sector area tool.
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Annulus (Ring) CalculatorCalculate the area and perimeter of an annulus (ring) from its outer and inner radii using Area = π(R² − r²) and circumference 2π(R + r).
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Regular Polygons Inscribed in a Circle CalculatorCompute side length and area of regular n-sided polygons inscribed in a circle of radius r, for a range of n, plus the circle area for comparison.
