Work out circle radius instantly with clear inputs, formula shown and shareable results.
The radius can be recovered from any one circle measurement: r = √(A/π) from area, r = C/(2π) from circumference, or r = d/2 from diameter.
From area
r = √(A / π)
From circumference
r = C / (2π)
√(78.539816 / π) = 5 exactly.
Circumference, because a tape around the object avoids having to locate the centre.