Calculator
Example Data Table
| Case | Known Input | Value | Pi Used | Circumference |
|---|---|---|---|---|
| Example 1 | Radius | 5 cm | 3.1416 | 31.4160 cm |
| Example 2 | Diameter | 12 m | 3.1416 | 37.6992 m |
| Example 3 | Area | 78.54 cm² | 3.1416 | 31.4159 cm |
| Example 4 | Radius | 2.5 ft | 22/7 | 15.7143 ft |
Formula Used
Circumference from radius: C = 2πr
Circumference from diameter: C = πd
Radius from area: r = √(A / π)
Arc length: L = (θ / 360) × C
Sector area: S = (θ / 360) × A
This page converts all inputs to a base unit internally, performs the calculation, then converts the outputs into your selected display unit.
How to Use This Calculator
- Select whether you know the radius, diameter, or area.
- Enter the numeric value and choose the input unit.
- Select the output unit for the final answers.
- Choose a pi option, including a custom value if needed.
- Enter a central angle when you also want arc length and sector area.
- Set decimal precision, then click the calculate button.
- Review the result cards, chart, and export buttons above the form.
Frequently Asked Questions
1) What does this calculator find?
It calculates circle circumference and also reports radius, diameter, area, arc length, and sector area. This makes it useful for classwork, drafting, measurement checks, and geometry practice.
2) Can I calculate using diameter instead of radius?
Yes. Choose diameter as the known input, enter its value, and the tool converts it into radius internally. Then it calculates the circumference and other related outputs.
3) What happens when I choose area as input?
The calculator first derives the radius using r = √(A / π). After that, it computes circumference, diameter, and the remaining measures from that derived radius.
4) Why is there a central angle field?
The angle lets you calculate arc length and sector area for part of a circle. Enter 360 degrees when you want the full circle only.
5) Can I change the value of pi?
Yes. You can use standard pi, 22/7, 3.14, or a custom value. This is useful for textbook methods, estimation, or matching specific engineering assumptions.
6) Does the calculator support unit conversion?
Yes. You can enter one unit and display the output in another. Area results are automatically shown in squared output units, while circumference stays in linear units.
7) What does the graph show?
The Plotly graph shows the linear relationship between radius and circumference. Your specific result appears as a highlighted point, helping you compare it with nearby circle sizes.
8) Can I save my results?
Yes. After calculation, use the CSV button for spreadsheet-friendly data or the PDF button for a clean report you can share, print, or archive.