Radius Diameter Circumference

Parts of circle:

Radius:
A line segment that goes from the center point to a point on the circle. Thus, it goes halfway through the circle.

Diameter:
A line segment that goes all the way across a circle through the center point.

Circumference:
The distance around the outside of the circle.
Finding radius, diameter, and circumference:
The diameter is always twice as long as the radius ; d = 2 x r.
Important formulas: C = 2 x Pi x r , C = Pi x d , d = C ÷ Pi
Pi(Pi) is a special number that occurs in circles. Its decimal places keep going and going, but we can use the approximation 3.14. So, in calculations, think Pi ? 3.14.