Circumference Calculator

The Circumference Calculator instantly finds the total distance around the edge of a circle given its radius, diameter, or area.

How It Works

Select your known variable: Radius ( $r$ ), Diameter ( $d$ ), or Area ( $A$ ).
Enter the numeric value.
The calculator applies Pi ( $\pi$ ) to solve for the exact circumference.

Formula & Calculation Logic

If you know the Radius: $C = 2 \pi r$

If you know the Diameter: $C = \pi d$

If you know the Area: $C = 2 \sqrt{\pi A}$

Worked Example

You have a circular pool with a diameter of 15 feet. $C = \pi \times 15$ $C \approx 3.14159 \times 15 \approx 47.12 \text{ feet}$ You will need roughly 47.12 feet of fencing to surround the pool.

Result Interpretation

Linear Distance: Circumference is a 1-dimensional measurement of length (e.g., inches, meters), unlike Area, which is squared.
Precision: The calculator uses highly precise floating-point math for Pi to ensure engineering-grade accuracy.

FAQs

What is Pi?

Pi ( $\pi$ ) is a mathematical constant representing the ratio of a circle's circumference to its diameter, approximately equal to 3.14159.

What is the difference between radius and diameter?

The radius is the distance from the center to the edge. The diameter is the distance straight across the circle, through the center. Diameter is exactly twice the radius.

Sources & Last-Reviewed Date

Sources: Standard Euclidean Geometry principles.
Last-Reviewed: 2026-09-03

Circumference Calculator