Pi (π) is a special mathematical constant. It is the ratio of any circle's circumference to its diameter. It is an irrational number, meaning its decimal representation never ends or repeats, but it's commonly approximated as 3.14 or 22/7.

October 2, 2025

What Is The Circumference Of A Circle

Q: What is the difference between circumference and area of a circle?

Circumference is the one-dimensional distance around the circle, measured in units of length (like inches or cm). Area is the two-dimensional space inside the circle, measured in square units (like square inches or cm²).

Q: Why are there two different formulas for circumference?

The two formulas, C = 2πr and C = πd, are essentially the same because the diameter (d) of a circle is always twice its radius (r). So, 2r can be substituted with d, making the formulas interchangeable.

Q: Is circumference always longer than the diameter?

Yes, for any circle, the circumference is always about 3.14159 times longer than its diameter. This constant relationship is the very definition of pi.

Learn the definition of the circumference of a circle. Understand the formula (C = 2πr) used to calculate the distance around a circle with a clear example.

Have More Questions →

Defining the Circumference of a Circle

The circumference of a circle is the total distance around its edge. It is the specific term for the perimeter of a circular shape. If you could cut the circle and lay it out as a straight line, its length would be the circumference.

Section 2: The Formula for Circumference

The circumference (C) is calculated using one of two related formulas. If you know the radius (r) of the circle, the formula is C = 2πr. If you know the diameter (d) of the circle, the formula is C = πd. The symbol π (pi) is a mathematical constant, approximately equal to 3.14159.

Section 3: A Practical Example

Imagine a pizza with a diameter of 14 inches. To find the length of its crust (the circumference), you would use the formula C = πd. The calculation would be C = π × 14 inches. The circumference is approximately 43.98 inches.

Section 4: Importance of Circumference

Calculating circumference is a fundamental concept in geometry with many real-world applications. It's used in engineering to design pipes and gears, in physics to understand circular motion, and in everyday tasks like measuring the amount of fencing needed for a circular garden or determining the distance a wheel travels in one rotation.

Frequently Asked Questions

What is the difference between circumference and area of a circle?

Why are there two different formulas for circumference?

What is pi (π)?

Is circumference always longer than the diameter?