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Circle Circumference Calculator

Circumference is the total linear distance around the outside edge of a circle (the perimeter of a circle). This free Circle Circumference Calculator

Mathematics
Formula & Methodology
Circumference = 2 × π × Radius = 2πr In terms of Diameter: Circumference = π × Diameter = πd

To compute the circumference of a circle: 1. Multiply the radius by 2 to find the full diameter across the circle. 2. Multiply the diameter by mathematical constant π (approx 3.14159). Because π is the ratio of any circle's circumference to its diameter, Circumference = π × d holds true for every circle in the universe.

Circumference (2πr)

43.9823

Overview

Circumference is the total linear distance around the outside edge of a circle (the perimeter of a circle). This free Circle Circumference Calculator computes the exact perimeter, diameter, and enclosed area from the radius.

Circumference is critical for determining bicycle and automotive wheel rotations per mile, fencing circular pens, ordering cylindrical piping insulation, and designing running tracks.

Worked Examples

Example 1: Circle with Radius = 7 inches

Input: Radius = 7

  1. Diameter = 2 × 7 = 14.
  2. Multiply by π: 14 × 3.14159 = 43.9823 inches.
Final Answer: 43.9823 linear units

Example 2: Bicycle Wheel Circumference (Radius 13 inches)

Input: Radius = 13 in (26" tire)

  1. Diameter = 26 inches.
  2. Circumference: 26 × 3.14159 = 81.68 inches per wheel revolution.
Final Answer: 81.68 inches

Example 3: Radius = 10 meters

Input: Radius = 10

  1. Circumference = 2 × π × 10 = 20π ≈ 62.8319 m.
Final Answer: 62.8319 linear units

How to Use This Calculator

  1. Enter the radius of the circle in the input box.
  2. Click "Calculate" to find the circumference.
  3. Review the diameter and enclosed area values below.
  4. Click "Reset" to evaluate another circular perimeter.

Reference Table

Radius (r)Diameter (d)Circumference (2πr)Enclosed Area
126.283.14
3618.8528.27
51031.4278.54
71443.98153.94
102062.83314.16

Frequently Asked Questions

What is the definition of Pi (π)?
Pi (π) is the universal mathematical constant defined as the ratio of any circle's circumference to its diameter: π = C / d ≈ 3.14159265.
How do you find the radius if you already know the circumference?
Divide the circumference by 2π: Radius = Circumference ÷ (2 × π).
What is the difference between circumference and perimeter?
Circumference is simply the specialized term for the perimeter of a curved circle.
In what units is circumference expressed?
Linear units such as inches, feet, meters, or centimeters (not square units).
Does doubling the radius double the circumference?
Yes. Because C = 2πr is a linear formula, doubling the radius exactly doubles the circumference.

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Reviewed & Authored by: Dr. Elizabeth Vance, PhD Applied Mathematics · Last Updated: 2026-10-06
Computed via exact circular circumference differential calculus.