Circumference to diameter calculator
Wrap a tape around a round object and you know its circumference. This tool turns that figure into the diameter, radius and area.
Loading the tool…
Processing and privacy: The result is calculated inside your browser and your data is not sent to any server.
How to use it
- Enter circumference and length unit.
- The result appears straight away and updates as you edit.
- Copy the result, or copy a link that keeps the same values to share it.
How it is calculated
Diameter = C ÷ π, radius = C ÷ (2π) and area = C² ÷ (4π), where C is the circumference.
Example
Inputs: Circumference = 100, Length unit = Centimeters (cm). Result: Diameter: 31.831 cm; Radius: 15.9155 cm; Area: 795.7747 cm².
Limits and caveats
- It assumes a perfectly round cross section; for oval trunks or objects the diameter is only an average.
- The unit choice only labels the results.
Questions about this tool
How do I get the diameter from the circumference?
Divide the circumference by π, about 3.1416. A circumference of 100 cm gives a diameter of about 31.83 cm.
Can I use it for a tree trunk?
Yes. Measure the girth at chest height and divide by π; that is the usual way to estimate trunk diameter.
How do I get the area straight from the circumference?
Area equals the circumference squared divided by 4π. The tool shows it next to the diameter.