Free · Circle geometry
Circle Circumference and Diameter Calculator
Convert the distance around a circle to its diameter, or calculate circumference from a known diameter, with length unit choices.
- Formula & worked example
- Private in your browser
- No signup
Calculator inputs
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How to use this calculator
- Enter the known values in the units shown. Results update as you type.
- Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
- Use the worked example to check the method. Reset restores the starting fields.
Private by default
Inputs and results stay in this browser tab. Bookify does not upload or store the values you enter.
Formula and method
A circle with diameter 1 has circumference pi, approximately 3.14159, in the same length unit.
C = pi*d; d = C/pi.
Worked example
Enter these known values and leave the other values blank.
- Diameter (d)
- 1 cm
- Circumference (c)
- 3.1416 cm
Assumptions and limitations
- Circumference is the complete circular boundary length, and diameter is the straight distance across the center. Both must be strictly positive.
- C = pi times d and d = C/pi. Choose a consistent length unit or let the retained unit selectors convert between units.
- The circle schematic is explanatory and not drawn to the entered scale. Clear the unknown before an inverse calculation; locked fields retain entered values.
Common questions
How do I find diameter from circumference?
Divide the circumference by pi. A circumference of 10 meters gives diameter 10/pi meters.
What is the difference between diameter and radius?
The diameter crosses the center between opposite points on the circle. The radius is half that distance.
References
Remove only the exact whole-capture-pinned empty trailing marketing group and its sole UI predicate, retaining every functional block and all numeric equations. Use strict positive circle dimensions.