Calculate circumference, radius, diameter, and area from any circle measurement
Circumference from Radius:
C = 2πr
where r is the radius
Circumference from Diameter:
C = πd
where d is the diameter
Area:
A = πr²
where r is the radius
Diameter:
d = 2r = C/π
diameter is twice the radius
Radius:
r = d/2 = C/(2π)
radius is half the diameter
The circumference is the distance around the circle - essentially its perimeter. It's calculated using the formula C = 2πr (using radius) or C = πd (using diameter), where π (pi) is approximately 3.14159.
The diameter is always exactly twice the radius. The radius is the distance from the center to the edge, while the diameter is the distance across the circle through the center. So d = 2r and r = d/2.
Pi is a mathematical constant representing the ratio of a circle's circumference to its diameter. This ratio is the same for all circles regardless of size. Pi is approximately 3.14159 and continues infinitely without repeating.
Circle calculations are used in countless applications: designing wheels and gears, calculating pizza sizes, determining pipe diameters, planning circular gardens or pools, astronomy, engineering, architecture, and many manufacturing processes.
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