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Circle calculator

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Input the area, circumference, radius or diameter of a circle, then choose a missing value. The calculator provides a step-by-step explanation on how to find the unknown dimension.

Circle Calculator
input value you know and select what to find
help ↓↓ examples ↓↓
Solve for
Enter one element of a circle.
Input the square root using the letter r ex: $3\sqrt{2} = \text{3r2}$. Type PI to input π.
area
A =
 
circ.
C =
radius
r =
 
diameter
d =
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Circle formulas
$$ A = r^2 \, \times \pi $$
area
$$ C = 2 \, r \, \pi $$
perimeter
$$ d = 2 \, r $$
diameter
examples
example 1:ex 1:
Find the area of the circle with a diameter of 6 cm.
example 2:ex 2:
Calculate the area of a circle whose circumference is C = 6π.
example 3:ex 3:
Calculate the diameter of a circle with an area of A = 9/4π.
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