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Choose what you know
Select radius, diameter, circumference, or area as the starting measurement.
Free Circumference Calculator
A circumference calculator finds the distance around a circle from its radius, diameter, area, or circumference. Enter one known measurement to calculate every circle value with unit conversions and formula steps.
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Circle calculator
Enter one known measurement
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Circumference result
62.8319 cm
For a circle with a 10 cm radius.
Radius
10 cm
Diameter
20 cm
Circumference
62.8319 cm
Area
314.1593 cm²
Step-by-step work
- 1. Find the radius with r = known radius.
- 2. Substitute the known value: r = 10 cm.
- 3. Calculate circumference: C = 2πr = 62.8319 cm.
- 4. Calculate area: A = πr² = 314.1593 cm².
How to Use the Circumference Calculator
2
Enter a value and unit
Add a positive value, choose its unit, and select a unit for the results.
3
Follow the formulas
Review every circle measurement plus the exact formulas and substitution steps.
Frequently Asked Questions
What is a circumference calculator?
A circumference calculator finds the distance around a circle. It can also solve the radius, diameter, and area from one known circle measurement.
How do you calculate circumference from radius?
Multiply the radius by 2π. The formula is C = 2πr, where r is the radius.
How do you calculate circumference from diameter?
Multiply the diameter by π. The formula is C = πd, where d is the diameter.
Can I find radius from circumference?
Yes. Divide the circumference by 2π. The formula is r = C / (2π).
Why are area units squared?
Area measures two-dimensional space, so it uses squared units such as cm² or in². Radius, diameter, and circumference use regular length units.