Is Circle Calculator Free? Free Web Tools, Core App Calculators, and Optional Pro
See what Circle Calculator offers free on the web and in the app, what optional Pro adds, and where to verify current subscription terms before paying.
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Measure twice. Understand why.
Worked geometry guides for people who need a result they can check: clear formulas, complete examples, practical mistakes, and a direct path to the matching calculator.
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How to Calculate a Truncated Cone Flat Pattern: Outer Radius, Inner Radius, and Sector Angle
Calculate a truncated-cone flat pattern from two diameters and height, with outer and inner radii, sector angle, arc lengths, area, checks, and limits.
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How to Calculate Semicircle Area, Arc Length, and Perimeter from Radius or Diameter
Calculate a semicircle's area, curved arc length, and full perimeter from radius or diameter, with exact formulas, a 20 cm example, and checks.
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How to Calculate Radius, Diameter, Circumference, and Area from Any One Value
Use one known radius, diameter, circumference, or area to calculate every other circle measurement, with inverse formulas, a worked 50 cm example, and checks.
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How to Calculate Sector Area, Arc Length, and Perimeter from Radius and Angle
Calculate sector area, arc length, and perimeter from radius and central angle, with degree and radian formulas, a worked example, and checks.
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How to Calculate Arc Length from Radius and Central Angle (Degrees or Radians)
Calculate arc length from radius and central angle in degrees or radians, with derivations, a worked 75° example, reverse formulas, and checks.
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How to Calculate Ring Area from Outer and Inner Diameter (Annulus Formula)
Calculate the area of a ring from its outer and inner diameters, with the annulus formula, a worked metric example, width, circumferences, and checks.
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How to Calculate Chord Length from Radius and Sagitta (Arc Height)
Find chord length from a circle’s radius and sagitta (arc height), with the formula, derivation, a worked example, input checks, and related arc results.
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How to Calculate Bolt Circle (PCD) Hole Coordinates: Formula, Example, and Common Mistakes
Calculate evenly spaced bolt-hole X/Y coordinates from PCD, hole count, start angle, direction, and center offset—with a worked 120 mm example.
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