Finding CircumferenceFinding Circumferencefor 4for 4thth and 5 and 5thth Grade Grade

By Andrea Klee

What Is CircumferenceWhat Is Circumference

Circumference is the distance all the way around a circle.

The equation to find circumference is 2r or multiplied by the diameter of the circle.

Some Terms DefinedSome Terms Defined is said as pie, like the kind you eat

– about 3.14

r is the radius of a circle – or half the distance across a circle

d is the diameter of a circle– or the distance all the way across a circle– or two radii added together

How To Find CircumferenceHow To Find Circumference

If you have the radius:– Multiply the radius by 2 to get the diameter.– Multiply this answer by 3.14 ( ).

If you have the diameter:– Multiply the diameter by 3.14 ().

Let’s Try A ProblemLet’s Try A Problem

Find the diameter or the radius.

We are going to find the radius.

What is the radius of this circle?

Problem ContinuedProblem Continued

The radius is 5.Next, multiply the radius by 2 to get the

diameter.

Last, multiply the diameter by or 3.14.

Problem SolvedProblem Solved

The circumference of the circle is 31.4.

Here’s Another ProblemHere’s Another Problem

Find the circumference of this circle.

SolutionSolution

The diameter is 6.

Multiply the diameter by (3.14).

The Circumference is 18.84.

LinksLinks

Math.com has everything you might want to know about the parts of circles.

This site defines circle, pie, circumference, diameter, and radius.

–  http://www.math.com/tables/geometry/circles.htm

LinksLinks

Prime Mathematics Enrichment is a magazine that has fun projects to do involving circles.

– http://www.nrich.maths.org.uk/prime/feb01/magazine.html

LinksLinks

Math Forum’s Ask Dr. Math This page is a letter sent to Dr. Math asking how

the circumference of the Earth was first measured. This offers a little history about circumference.

– http://mathforum.org/library/drmath/view/58988.html