Circle Calculator
Given the radius, diameter, circumference or area of a circle, find all of the others at once.
Runs 100% in your browser — nothing is uploaded.
Result
Formula
d = 2r · C = 2πr · A = πr²
About this calculator
The Circle Calculator computes the radius, diameter, circumference, and area of a circle when any one of these values is known. It is designed for quick and accurate conversions between these fundamental circle measurements.
How to use
- 1
Choose which value you know.
- 2
Enter it.
- 3
Read all four circle measurements.
Frequently asked questions
What is the relationship between radius and diameter?
The diameter is twice the radius: d = 2r. Conversely, the radius is half the diameter: r = d/2.
How is the circumference calculated?
The circumference is calculated using the formula C = 2πr, where r is the radius. It can also be expressed as C = πd.
How is the area of a circle calculated?
The area is calculated using the formula A = πr², where r is the radius. Alternatively, it can be expressed as A = π(d/2)².
Please note: Results are estimates for general information only and are not professional or medical/financial advice.