Math

Instant, private, and free

Circumference to Diameter Calculator.

Convert a circle circumference to its diameter using d = C / π.

On-device calculationNo signup
01

Set your values

Results update as you type.

Diameter: 9.999992 units

Diameter

0.000000units

Results update automatically as you type.

Use Cases

Find the diameter of a circular object

If you know the circumference of a circle (e.g., a tree trunk, pipe, or wheel), use this calculator to quickly find its diameter without manual calculation.

Example: A tree with a circumference of 100 cm has a diameter of about 31.83 cm.

Check your math homework

Verify your manual calculations for circle geometry problems by entering the circumference and comparing the computed diameter.

Example: For a circumference of 50 units, the diameter is approximately 15.92 units.

Frequently Asked Questions

How do I convert circumference to diameter?
Use the formula d = C / π, where C is the circumference and π (pi) is approximately 3.14159. Simply divide the circumference by pi to get the diameter.
What units can I use for the circumference?
You can enter the circumference in any unit you choose, such as inches, feet, centimeters, meters, or any other unit. The calculator will output the diameter in the same unit.
Why is the diameter equal to circumference divided by pi?
The circumference of a circle is π times the diameter (C = πd). Rearranging this formula gives d = C / π, so dividing the circumference by pi yields the diameter.

Tips & Common Mistakes

Tips

  • Ensure the circumference value is positive; a negative or zero circumference is not physically meaningful for a real circle.
  • Use consistent units for circumference and diameter; the calculator outputs the diameter in the same unit you enter.
  • For more precise results, use a high-precision value of π (e.g., 3.141592653589793) if you are doing manual checks.
  • If you have the radius instead, remember that diameter = 2 × radius, so you can double the radius to get the diameter directly.

Common Mistakes to Avoid

  • Forgetting to divide by π and instead multiplying the circumference by π, which gives the area-related value, not the diameter.
  • Using the radius in place of the circumference; the calculator expects the circumference, not the radius.
  • Entering the circumference in one unit and expecting the diameter in a different unit without converting.

Last updated: August 13, 2026