How do you convert circumference to diameter?
Divide by π.
Circumference to Diameter Calculator
Turn circumference into diameter (and radius) with a single division by π.
Enter circumference
Provide a positive circumference C.
About this calculator
How to use Circumference to Diameter Calculator, plus the formulas and logic behind the results.
Tool description
Because C = πd, diameter is circumference divided by π. Radius is half the diameter.
How to use
- Enter a positive circumference.
- Select Calculate.
- Read diameter and radius.
- Optionally check C ≈ πd.
Formulas & reference
d = C / πr = C / (2π)
Quick conversions
- C = π → d = 1
- C = 2π → d = 2
- r = d/2
- Uses M_PI
Calculation logic
Divides by M_PI (and 2π for radius) after validating C > 0.
Useful when a measuring tape wraps a circular object.
Circumference to Diameter Calculator FAQ
Common questions about this calculator and how to use the results.
How do you get radius?
Divide circumference by 2π, or halve the diameter.
What π is used?
M_PI.
Can C be zero?
No—enter a positive circumference.
Is this exact?
It is exact relative to the π constant used by the calculator.
Does this work for arcs?
No—use full circumference, not an arc length.