Inputs
Adjust the assumptions to match your scenario. Results update instantly.
Results
Primary outputs and comparison insights are built from the current inputs.
Diameter
16
Full width of the circle from edge to edge through the center.
Circumference
50.27
Distance around the full circle.
Area
201.06
Area covered by the full circle.
Sector area
50.27
Area covered by the selected sector percentage.
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How this Circle Calculator works
The Circle Calculator gives you diameter, circumference, full area, and sector area from a radius so you can solve everyday geometry tasks quickly. Enter radius and sector percent to estimate diameter, circumference, and area. The calculator updates instantly and adds a comparison table plus chart so you can test the sensitivity of the result before you use it in a decision.
Quick guide
Jump to the section you need, then return to the circle calculator.
Inputs
- Radius of the circle used for all geometry outputs.
- Percentage of the full circle used for the sector area.
Outputs
- Full width of the circle from edge to edge through the center.
- Distance around the full circle.
- Area covered by the full circle.
- Area covered by the selected sector percentage.
Assumptions
- The shape is a perfect circle.
- Sector area uses the selected percentage of the full circle.
Tips
- Radius changes affect area much faster than circumference.
- Use sector area when you only need part of the full circle.
Circle Calculator formula guide
Use these circle calculator formulas to audit the output or explain it to someone else.
2 formulas
Circle Calculator examples
Review a ready-made circle calculator scenario, copy it, then tweak inputs to match your case.
Example
Round table sizing
Inputs
- Example input Radius: 6
- Example input Sector percent: 50%
Outputs
- Example result Diameter: 12
- Example result Circumference: 37.7
- Example result Area: 113.1
- Example result Sector area: 56.55
Circle formulas are simple but easy to misread if diameter and radius get mixed up, so keep the unit and input type clear.
Circle measures by radius
| Radius | Circumference | Area |
|---|---|---|
| 5 | 31.42 | 78.54 |
| 7 | 43.98 | 153.94 |
| 8 | 50.27 | 201.06 |
| 10 | 62.83 | 314.16 |
| 12 | 75.4 | 452.39 |
Area grows with the square of the radius, so even small radius changes can create large area differences.
Area growth by radius
Focus point
5
78.54
Position
#1 of 5
Original order
Share of total
6.54%
Total: 1,200.09
Area grows with the square of the radius, so even small radius changes can create large area differences.
References
- Basic circle geometry formulas
- Sector area calculations in elementary geometry
Learn more
Guides connected to the circle calculator
Use these short guides when you want the decision framework behind the numbers, not just the raw output.
Category guide
Math Calculator Guide
Pick the right math calculator by problem type: arithmetic, ratios, coordinates, geometry, or measurement.
Directly related
Articles that mention this calculator
FAQ
Circle Calculator FAQ
What does the Circle Calculator do?
The Circle Calculator gives you diameter, circumference, full area, and sector area from a radius so you can solve everyday geometry tasks quickly. Enter radius and sector percent to estimate diameter, circumference, and area. The calculator updates instantly and adds a comparison table plus chart so you can test the sensitivity of the result before you use it in a decision. It is part of our math toolkit.
What inputs do I need?
Typical inputs include Radius of the circle used for all geometry outputs., Percentage of the full circle used for the sector area..
How are the results calculated?
We follow the formulas and assumptions outlined in the "How this calculator works" section. You will see outputs like Full width of the circle from edge to edge through the center., Distance around the full circle., Area covered by the full circle..
Can I share or download the results?
Use the Copy link or Print buttons to share your results. If a table or chart appears, you can download the data as CSV.
Is my data stored?
No. Calculations run in your browser and we do not store your inputs.
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