Frequently Asked Questions
Everything you need to know about the Circle Calculator.
What can I enter?
Any one of radius, diameter, circumference, or area — the rest are calculated automatically.
How does it find radius from area?
It rearranges A = πr² to r = √(A/π) and solves.
Does it show exact values?
Yes, results are shown as exact π-expressions (e.g. 25π) alongside decimals.
What is arc/sector mode?
Given a radius and central angle, it calculates arc length, sector area, and chord length for that slice.
Does it show the formulas used?
Yes, each calculation shows the formula and the algebra involved.
What angle units does arc mode accept?
Both degrees and radians, selectable via toggle.
What if I enter a negative or zero value?
It's rejected with a clear message, since radius/diameter/area/circumference must be positive.
Does it work with any unit (cm, inches, etc.)?
Yes, the calculator is unit-agnostic — just be consistent with your own units.
Is it free?
Completely free, no sign-up or limits.
Does it work on mobile?
Yes, fully responsive.