How to figure out the circumference of a circle?
Understand the Problem
The question is asking for the method to calculate the circumference of a circle. The circumference is the distance around the circle, and it can be calculated using the formula C = 2πr, where r is the radius of the circle.
Answer
C = 2πr
Answer for screen readers
To figure out the circumference of a circle, you need to use the formula C = 2πr, where C is the circumference, π (pi) is approximately 3.14159, and r is the radius of the circle.
Steps to Solve

Identify the formula
The formula for the circumference of a circle is:
$C = 2πr$
Where:
 C is the circumference
 π (pi) is approximately 3.14159
 r is the radius of the circle

Determine the radius
Measure or identify the radius of the circle. The radius is the distance from the center of the circle to any point on its edge.

Apply the formula
Substitute the values into the formula and calculate:

Multiply the radius by 2

Multiply the result by π (3.14159)
For example, if the radius is 5 units:
$C = 2 × π × 5$ $C ≈ 2 × 3.14159 × 5 ≈ 31.4159$ units
To figure out the circumference of a circle, you need to use the formula C = 2πr, where C is the circumference, π (pi) is approximately 3.14159, and r is the radius of the circle.
More Information
The ratio of a circle's circumference to its diameter is always π, regardless of the circle's size. This constant relationship is what makes π such an important number in mathematics and many scientific fields.
Tips
Common mistakes include confusing the radius with the diameter (which is twice the radius) or using an incorrect value for π. Always make sure you're using the radius in the formula, and use 3.14159 or the π button on a calculator for more precise calculations.