Perimeter of a Circle Calculator

Summary

Enter a radius or diameter to instantly get the circumference of a circle with a full formula breakdown.

How it works

1. Choose whether you are entering a radius or a diameter.
2. Type the measurement value in the input field.
3. Optionally enter a unit label (cm, m, in, ft, etc.) for display.
4. The calculator applies C = 2πr (or C = πd) and shows the result instantly.
5. The formula breakdown section walks through each arithmetic step.
6. Adjust the decimal precision slider to control how many digits are shown.

Use cases

• Calculate the length of fencing needed around a circular garden or pool.
• Find the total distance around a circular track or running path.
• Determine the amount of trim or edging required for a round table.
• Verify engineering measurements for circular pipes, wheels, or gears.
• Solve geometry homework problems involving circle circumference.
• Convert between radius, diameter, and circumference quickly.
• Cross-check CAD measurements for circular parts or features.

Frequently Asked Questions