Circle Calculator
Calculate the area and circumference of a circle from its radius.
Calculate
Enter your values below.
Result
Area
0
Circumference
0
Formula used
Area = πr², Circumference = 2πr
Example: Radius 7 → area ≈ 153.94, circumference ≈ 43.98.
How to use this calculator
- Enter Radius.
- Press Calculate to see your result instantly.
FAQ
Frequently asked questions
What if I only have the diameter?
Divide the diameter by 2 to get the radius before entering it here.
What value of π is used?
JavaScript's built-in Math.PI, accurate to about 15 decimal digits.
What units is the result in?
Area is in your unit squared; circumference is in the same linear unit.
Can radius be zero?
A radius of zero isn't a real circle, so please enter a positive value.