C=2πr, A=πr²Radius determines diameter, circumference and area.
Geometry & measurement
Circle calculator
Find diameter, circumference and area from radius.
LocalFree
Study & learning use only
Use the result as a learning aid and verify important calculations against your course material or instructor.
Use the result as a learning aid and verify important calculations against your course material or instructor.
This tool runs on your device in the browser.
Instructions and limitations
TOOL GUIDE
What this tool is for
Circle calculator — Find diameter, circumference and area from radius.
Useful for practice, understanding the method, and checking homework steps where outside tools are allowed.
Common uses
- Practice a formula or method
- Check your working
- Review before a lesson or exam
Study and learning use only
Use the result for practice and understanding, not as a guaranteed answer. Verify important calculations and follow your school, university, and academic-integrity rules.
EXPLANATION & EXAMPLE
Understand the result—not just the number
Use the starting values, then change one input to see its effect.After calculating, the tool shows the values used and the working so you can check it.