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Circumference of a Circle Calculator

Enter any one measure of a circle — radius, diameter, circumference or area — and get the other three instantly, with every formula shown with your numbers substituted in.

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Reading the known value
Solving for the radius
Computing the other measures

Result

This page opens the circle calculator with the diameter preselected as the known value and the circumference as the highlighted answer. Type the diameter, press the button, and you get the distance around the circle together with the formula written out with your number in it.

The circumference is the diameter multiplied by π: C = πd. A dinner plate 26 across has a circumference of π × 26 ≈ 81.68; a circular running track 100 across measures about 314.16 around. If you have the radius instead, switch the known value — the formula becomes C = 2πr and the result is the same.

The calculator also fills in the radius and the area at the same time, so one measurement answers every follow-up question. Everything is computed locally in your browser, and the copy button grabs all four values at once.

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Executed in Browser

Your files and inputs never leave this device. Processing runs completely offline. 100% Secure.

Accepted Formats & Rules

  • Solves from any of the four known values: radius, diameter, circumference or area.
  • Shows each formula with substitution, e.g. C = 2πr = 2 × π × 5 ≈ 31.415927.
  • Exact answers in terms of π (like A = 25π) whenever the radius or diameter is given.
  • Copy button grabs all four measures in one click.

Key Benefits

✓ One input is enough: give any single measure and the radius, diameter, circumference and area all appear at once.
✓ Every result comes with the formula written out with your numbers substituted — ideal for showing your work in homework.
✓ Runs entirely in your browser: no sign-up, no upload, instant results.

Use Cases

  • • Find how much edging or fencing a round flower bed needs from its measured diameter.
  • • Get the exact answer in terms of π, like A = 25π, for geometry homework — with every formula substituted step by step.
  • • Convert a tape measurement around a trunk, pipe or column into its diameter and cross-section area.