Circumference of a circle
Diameter of a circle The circumference of a circle is the length of the red line in the picture. The circle circumference is the diameter multiplied by pi. The area of a circle is the circumference multiplied by 1/4 of the diameter.


Exercises
  1. How much is the circumference of a circle when the diameter is 5?
  2. What is the circumference of a circle with radius 10?
  3. The surface area of a circle equals 500. What is the circumference?
  4. What is the diameter of a circle with circumference 1109?
  5. A vehicle has 60 cm diameter wheels which make 30 revolutions per second. Calculate the speed in kilometers per hour.
Solutions
  1. 5*π = 15,7
  2. 2*10*π = 62,8
  3. The diameter equals 25,2, so the circumference equals 79,3.
  4. 353
  5. Velocity = 30 * 0,60 * π = 56,5 meters per second = 204 km/h.

You might want to have a look at our other pages about math, geometry, figures and volumes!