Math · FREE CALCULATOR
Circle Calculator
Calculate circle area, circumference, and diameter from radius. Change the sample numbers to get an instant estimate tailored to your situation.
Your inputs
Adjust any value to update the results.
Calculated results
Based on your current inputs
Calculating…
How this calculator works
Enter the radius using any consistent length unit. Area uses squared units.
Formula
Area = πr²; circumference = 2πr.
Before you use the result
Calculator outputs are estimates based on the numbers you provide. Replace the examples with measurements, costs, rates, or product information appropriate to your situation.
Keep in mind
The input unit is user-defined; use one unit consistently.