Calculate the circumference of a circle

Circumference is the distance around a circle, related to its radius and diameter by $C=2\pi r=\pi d$ , where $\pi$ represents the constant ratio of circumference to diameter. The learner calculates circumference from a given radius or diameter, selects an appropriate approximation for $\pi$ , reports a measurement in linear units, and distinguishes circumference from area; advanced derivations and formal error analysis are not included.

Detailed Explanation: Calculate the circumference of a circle

The circumference is the distance around a circle. Use one of these formulas:

If you know the radius: $C=2\pi r$
If you know the diameter: $C=\pi d$

Here, $C$ is circumference, $r$ is radius, and $d$ is diameter. Use $\pi\approx 3.14$ unless your teacher asks you to use a calculator’s $\pi$ button. The answer must be in linear units, such as centimeters or meters.

Example

A circular garden has a diameter of $8$ meters. Find its circumference.

Step 1: Choose the formula.

The diameter is given, so use

C=\pi d

Step 2: Substitute the known values.

Use $\pi\approx 3.14$ and $d=8$ :

C\approx 3.14(8)

Step 3: Multiply.

C\approx 25.12

Step 4: Include the units.

The circumference is

\boxed{25.12\text{ meters}}

This is the distance around the garden. It is not the area, which measures the space inside the circle and would be given in square units, such as $\text{m}^2$ .

Learn by doing: Calculate the circumference of a circle

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Circumference

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