Circle Calculator
Find a circle radius, diameter, circumference, and area from any one known value. Fast and private.
Independently verified for accuracy
Calculator by Toolsloft ↗- Radius
- 5
- Diameter
- 10
- Circumference
- 31.415927
- Area
- 78.539816
Work out every measurement of a circle from any one you already know. Enter the radius, diameter, circumference, or area, and get all four back. Useful for geometry, DIY projects, and layout planning.
How this is calculated
The tool first recovers the radius from whatever you enter: half the diameter, the circumference divided by 2 pi, or the square root of the area divided by pi. It then computes diameter as 2 times the radius, circumference as 2 pi times the radius, and area as pi times the radius squared, using the value of pi built into your browser.
How to use
- Choose which measurement you know: radius, diameter, circumference, or area.
- Enter its value.
- Read the radius, diameter, circumference, and area.
Examples
- From radius:
Radius 5 gives area 78.539816 - From diameter:
Diameter 10 gives the same circle as radius 5
FAQ
- How do I find the area of a circle?
- Multiply pi by the radius squared. For a radius of 5 that is pi times 25, which is about 78.54.
- Can I start from the circumference or area?
- Yes. Pick which value you know and the tool recovers the radius first, then reports the diameter, circumference, and area for that same circle.