Calculators
Circle Calculator
Calculate circle area, circumference, and diameter from a radius locally in your browser.
Enter a radius from 0 to 1000000000 to see the area (πr²), circumference (2πr), and diameter (2r). The calculation runs locally in your browser; your value is not uploaded or stored.
Find circle measurements without uploading anything.
Enter a radius from 0 to 1000000000 to see the area, circumference, and diameter. Everything runs locally in your browser, so your value is not uploaded or stored.
Frequently Asked Questions
Everything you need to know about this tool, how it works, and privacy.
What does the circle calculator show?
Enter a radius from 0 to 1000000000. The calculator returns the area (pi times r squared), the circumference (2 times pi times r), and the diameter (2 times r). For example, a radius of 5 gives an area of about 78.5398163397, a circumference of about 31.4159265359, and a diameter of 10.
Which formulas does the circle calculator use?
It uses area = pi x r^2, circumference = 2 x pi x r, and diameter = 2 x r, where r is the radius you enter and pi is the standard mathematical constant.
Which inputs are accepted?
Enter a radius from 0 to 1000000000. Zero is valid and gives zero for every measurement. Decimal values are accepted. Negative numbers, non-numeric text, and values above the limit show a clear error instead of a result.
Do my numbers stay private?
Yes. The calculation and copy action run locally in your browser. CodeASystem does not upload or store the value you enter.