FREE BROWSER TOOLGeometry
Circle Calculator — Radius, Diameter, Circumference and Area
Choose the dimension you can measure. For a circular tabletop, its width through the center gives you both the length of edge trim and the surface area to cover.
Calculations run in your browser. No account or API key is needed.
Your result
Edit inputs- Radius
- 12 cm
- Diameter
- 24 cm
- Circumference
- 75.39822369 cm
- Area
- 452.3893421 cm²
Radius = 12 cm Diameter = 24 cm Circumference = 75.39822369 cm Area = 452.3893421 cm²
How to use this tool
Choose radius, diameter, circumference or area.
Enter a positive value and choose the length unit. An area measured in cm² uses cm as its length unit.
Update the result and read the dimensions in the selected unit.
Measure a round object
A 24 cm diameter tabletop has a radius of 12 cm. Its edge measures 24π cm, about 75.4 cm, and its top covers 144π cm², about 452.4 cm². If you measure the edge with a tape instead, choose circumference.
Work backward to the radius
Starting with diameter d gives r = d / 2. From circumference C, use r = C / (2π). From area A, use r = √(A / π). Once the radius is known, the area is πr² and the circumference is 2πr.
Common questions
Where should I measure the diameter?
Place the ruler from one edge to the opposite edge on a straight line through the center. Moving that line away from the center makes the measurement shorter.
How should I round the result?
The calculator displays up to ten significant digits. Match the precision of your original measurement when you report a physical size. A diameter measured to the nearest centimeter rarely supports an answer to a fraction of a millimeter.