Facts About the Circle

1. A circle is a 2D shape made of all points that are the same distance from a fixed point called the center.
2. The distance from the center to any point on the circle is called the radius (r).
3. The distance across the circle through the center is the diameter (d).
4. The diameter is always twice the radius: $$d = 2r$$d=2r
5. The line around a circle is called the circumference.

Important Circle Formulas

6. Circumference: $$C = 2\pi r \quad \text{or} \quad C = \pi d$$C=2πrorC=πd
7. Area: $$A = \pi r^2$$A=πr2
8. The symbol π (pi) is approximately 3.14159.

Angle & Arc Facts

9. A circle contains 360 degrees.
10. A semicircle is half a circle (180°).
11. A quarter circle is 90°.
12. An arc is a portion of the circle’s edge.
13. A chord is a line segment connecting two points on a circle.
14. The diameter is the longest chord in a circle.
15. A tangent touches a circle at exactly one point.

Fun & Interesting Facts

16. A circle has infinite lines of symmetry.
17. A circle has no corners and no sides.
18. The ratio of circumference to diameter is always π.
19. Among all shapes with the same perimeter, the circle encloses the largest area.
20. Circles appear everywhere in real life — wheels, coins, clocks, planets, bubbles, and ripples in water.

• February 2025

ScienceCalx