DocomintCalculatrice de Cercle
Calculez le rayon, le diamètre, la circonférence et l'aire d'un cercle à partir de n'importe quelle valeur connue.
What is a Calculatrice de Cercle?
Most circle calculators assume you're starting from the radius, but real problems often hand you the circumference (a tape measure around a pipe) or the area (a spec sheet) instead — this works backward from any of the four values to fill in the other three.
How to use the Calculatrice de Cercle
- Choose which value you already know — radius, diameter, circumference, or area
- Enter that value
- The other three values appear instantly, computed on your device
Formula
Area = πr² | Circumference = 2πr | Diameter = 2r
Whichever one value you provide, the tool solves for radius first, then derives the other three from it.
Example
A circular table with a 113.1 in² tabletop (area known) works out to a radius of about 6 inches, a 12-inch diameter, and a circumference of about 37.7 inches — handy for figuring out the diameter without being able to measure straight across the middle.
Common mistakes
- Entering the diameter's value but leaving "Known value" set to Radius — that treats the diameter as if it were the radius and doubles every downstream result incorrectly.
- Squaring the diameter instead of the radius when computing area by hand — the area formula uses radius, not diameter.
- Mixing up circumference (2πr, a length) with area (πr², a squared measurement) since both involve π.
Frequently asked questions
How do I find a circle's area if I only know the circumference?
First solve for radius: r = circumference / (2π). Then compute area = π × r². Select "Circumference" as the known value here and it handles both steps for you.
What's the difference between radius and diameter?
Radius is the distance from the center of a circle to its edge. Diameter is the distance all the way across, through the center — always exactly twice the radius.
What if I only know the area?
Set "Known value" to Area and enter it — the tool solves radius = √(area ÷ π) first, then derives diameter and circumference from that.
How precise is π in this calculator?
It uses JavaScript's built-in Math.PI, accurate to about 15 significant digits — far more precision than any real-world measurement input would need.
Is my numbers uploaded anywhere?
No — Calculatrice de Cercle runs entirely in your browser using JavaScript/WebAssembly. Your numbers is never sent to a server.