A simple way to find the radius of a circle if you know the circumference of the circle

The example below illustrates clearly how to find the radius of a circle when the circumference is known. Suppose the circumference of a circle is 50.24 inches, calculate r.


find the radius of a circle given circumference

Here are the steps to follow:

Step 1:

Write down the circumference formula.

Step 2:

Replace the circumference with 50.24 inches.

Step 3

Since you are looking for r, you need to get rid of 2 × pi. You do this by dividing both sides by 2 × pi.

Step 4

Notice that now the number next to r is just 1 and 1 times r is r. To get the answer, you just have to divide 50.24  inches by 6.28. When the circumference of a circle is 50.24 inches, the radius is 8.

The example above illustrates a simple but long way to solve this problem. You can find the radius of a circle very quickly by dividing the value of any circumference by 6.28.

Example 2:

Find r when the circumference is 31.4

r = 31.4 / 6.28 = 5.

Yes, it is that simple yet you still need to know how to do it by following the steps above.

Recent Articles

  1. Factoring trinomials of the form x^2 + bx + c

    Jul 03, 20 09:51 AM

    factoring trinomials (ax^2 + bx + c ) when a is equal to 1 is the goal of this lesson.

    Read More

New math lessons

Your email is safe with us. We will only use it to inform you about new math lessons.

                                 Follow me on Pinterest

Real Life Math Skills

Learn about investing money, budgeting your money, paying taxes, mortgage loans, and even the math involved in playing baseball.