Choose the known parameter – radius, diameter, area, or circumference.
Enter its value – the label changes to match your selection.
Instant results – the other three values are calculated using standard circle formulas:
r = d/2 = √(A/π) = C/(2π)
d = 2r = 2√(A/π) = C/π
A = πr² = π(d/2)² = C²/(4π)
C = 2πr = πd = 2√(πA)
Copy or download PDF – save your circle measurements.