Circle. Radius, Diameter and Circumference The Radius is the distance from the center to the edge. The Diameter starts at one side of the circle, goes through the center and ends on the other side. The Circumference is the distance around the edge of the circle. And here is the really cool thing: When you divide the circumference by the diameter you get 3.141592654... which is the number π ( Pi ) We can say: Circumference = π × Diameter Example: You walk around a circle which has a diameter of 100m, how far have you walked? Also note that the Diameter is twice the Radius: Diameter = 2 × Radius And so this is also true: Circumference = 2 × π × Radius Remembering The length of the words may help you remember: Radius is the shortest word Diameter is longer (and is 2 × Radius) Circumference is the longest (and is π × Diameter) Definition Area The area of a circle is π times the radius squared, which is written: A = π × r 2 Or, in terms of the Diameter: A = ( π /4) × D 2 A = π × r 2 A = π × 1.2 2 A = π × (1.2 × 1.2)
Circles: Radius, Diameter and Circumference. Circles 1 - Circumference and Area. Area of a Circle - VividMaths.com. Circles Part 3- Degrees vs. Radian Measure and Cycles or Sine Waves - Eeris Fritz. Circles Part 2- Understanding Area - Eeris Fritz. Circles Part 1- Understanding Pi, Diameter, Radius and Circumference - Eeris Fritz.