How to Calculate Circle
What is Circle?
A circle is the set of all points in a plane that are exactly the same distance (the radius) from a central point. All four measurements — radius, diameter, circumference, and area — can be calculated from just one known value using the mathematical constant π (pi ≈ 3.14159).
Step-by-Step Guide
- 1Radius (r): the distance from the centre to any point on the circle
- 2Diameter (d): twice the radius — d = 2r
- 3Circumference (C): the perimeter of the circle — C = 2πr = πd
- 4Area (A): the space enclosed — A = πr²
Worked Examples
Input
r = 5
Result
d=10, C=31.416, A=78.540
All from one given value
Input
C = 100
Result
r=15.915, d=31.831, A=795.775
Working back from circumference
Input
A = 200
Result
r=7.979, d=15.959, C=50.133
Working back from area
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