Circle calculators
12 calculators Arc Length Calculator Calculate arc length, chord, sector area, sagitta and perimeter from radius and central angle in degrees or radians. Reverse-solve for radius or angle.
Open Area of a Circle Calculator Find circle area from radius, diameter, circumference, or area. Includes sector area, annulus area, unit switch, exact-pi output, and a full worked solution.
Open Circle Calculator Solve any circle from radius, diameter, circumference, or area. Get all four properties, exact pi form, sector area and arc length in any unit.
Open Circumference Calculator Find circumference, area, radius, diameter, arc length, and sector area from any one circle measurement. Metric and imperial units, with step-by-step working.
Open Sector Area Calculator Calculate sector area, arc length, chord length, and segment area from radius and central angle. Supports degrees or radians, metric or imperial, and reverse-solve.
Open Circle Theorems Calculator Calculate inscribed angles, central angles, arc lengths, chord lengths, cyclic quadrilateral angles, and secant-tangent relationships with step-by-step working.
Open Coin Rotation Paradox Calculator Calculate how many times a rolling coin rotates around a fixed coin. Covers external and internal rolling, any radius ratio, with step-by-step math and worked examples.
Open Equation of a Circle Calculator Find the equation of a circle in standard, general, and parametric form. Enter center and radius, three points, or general-form coefficients for instant step-by-step results.
Open Semicircle Area Calculator Calculate semicircle area, perimeter, arc length, radius and diameter instantly. Enter any one value and get all the rest, with step-by-step working.
Open Square in a Circle Calculator Calculate the largest square inside a circle, largest circle inside a square, or find equal-area equivalents. Instant results with step-by-step formulas.
Open String Girdling Earth Calculator: Gap and Extra Length Calculate the extra string needed to raise a rope around Earth by any gap, or find the gap from the extra length. Formula, steps, and worked examples included.
Open Tangent of a Circle Calculator Calculate the tangent length from an external point to a circle, the angle between tangents, and two-circle external and internal tangent lengths. Full worked steps.
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