Work out a circle’s area, circumference and more from its radius. Enter one measurement and get the rest instantly.

Circle Calculator

Solve radius, diameter, circumference, and area of any circle from a single known measurement — with both decimal approximations and exact multiples of π.

Solve from any 1 value Exact π & decimal forms Save PDF · PNG · Share cm, m, in, ft units

Circle measurement

Pick which property you know and enter its value.

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TinyExe Circle Calculator tinyexe.comFree online calculators

TinyExe · Circle Result

Radius, diameter, circumference & area

Calculated on
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– Area
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BMI Prime — · Healthy range for your height: —

Name

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Radius (r)

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Diameter (d)

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Circumference

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How this was calculated

    What to do next

      TinyExe · tinyexe.com — Calculations use full IEEE 754 double-precision π (3.141592653589793) before rounding for display.

      TinyExe PDF & PNG exports carry the TinyExe logo and tinyexe.com header & footer.

      Calculations use full IEEE 754 double-precision π (3.141592653589793) before rounding for display.

      Embed this tool

      Add this Circle Calculator to your own page — copy the code below and paste it where you want the tool to appear.

      The embed loads the live calculator in a frame, so it stays up to date automatically. Choose a width, check the code, then copy it. When you publish on WordPress, keep the src pointing at your live tool URL.

      Works in WordPress (Custom HTML block), HTML pages, and most site builders.

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      Circle relationships from any known value

      Knowing any one property of a circle uniquely determines the other three.

      Given Radius (r) Circumference (C) Area (A)
      Radius (r) r 2πr
      Diameter (d) d ÷ 2 πd
      Circumference (C) C ÷ (2π) C
      Area (A) √(A ÷ π) 2√(πA)

      The formula

      The two fundamental circle formulas in plane geometry.

      Area of a Circle

      A = π × r² (or π × d² ÷ 4)

      Square the radius and multiply by π (≈ 3.14159265). Area is always expressed in square units (cm², m², in²).

      Circumference of a Circle

      C = 2 × π × r (or π × d)

      The perimeter distance around the circle is π times the diameter (or 2π times the radius).

      Worked examples

      Three circle calculations showing both exact π and decimal answers.

      Example 1 · From Radius

      Radius r = 10 cm

      Finding diameter, circumference, and area.

      CalculationSteps
      C = 2π(10) = 20πCircumference ≈ 62.832 cm.
      A = π(10²) = 100πArea ≈ 314.159 cm².

      A = 314.16 cm²

      Example 2 · From Diameter

      Diameter d = 14 in

      Finding area of a 14-inch circle.

      CalculationSteps
      r = 14 ÷ 2 = 7 inHalf of diameter gives radius.
      A = π(7²) = 49πArea ≈ 153.938 in².

      A = 153.94 in²

      Example 3 · From Area

      Area A = 78.54 m²

      Working backward to find radius and circumference.

      CalculationSteps
      r = √(78.54 ÷ π) ≈ 5 mDivide area by π and take square root.
      C = 2π(5) ≈ 31.42 mPerimeter of the circular plot.

      r = 5.00 m

      How to use this calculator

      Select the measurement you know

      Choose Radius, Diameter, Circumference, or Area.

      Enter the number and unit

      Type your positive measurement and pick cm, m, mm, in, or ft.

      Press Calculate Circle

      Read all four circle properties in decimal and exact π notation.

      Scaling rule: If you double a circle's radius, its circumference doubles, but its area increases by a factor of 2² = 4.

      Frequently asked questions

      How do you find the area of a circle from its diameter?

      Divide the diameter by 2 to get the radius, square that radius, and multiply by π (or compute π × d² ÷ 4 directly).

      How do you find the radius from the circumference?

      Divide the circumference by 2π (approximately 6.283185).

      Circle Calculator — Euclidean geometry solver. Exact π and decimal outputs.