Circle Length
Calculate the circumference of a circle from its radius using the formula C = 2pir. Free online geometry tool for students, teachers, and professionals.
About This Calculator
This calculator computes the circumference (distance around a circle) from its radius using the formula C = 2pir. Simply enter the radius value in any unit (cm, m, inches, feet) and get the circumference in the same unit instantly. This tool is useful for geometry homework, engineering layouts, construction projects, and any application requiring circle measurements.
Frequently Asked Questions
What is the formula for the circumference of a circle?
The circumference C of a circle is calculated using C = 2pir, where r is the radius of the circle. Alternatively, if you know the diameter d, you can use C = pid.
What is the difference between circumference and diameter?
The diameter is the straight-line distance across the center of a circle, while the circumference is the distance around the outer edge. The circumference is always approximately 3.14159 (pi) times the diameter.
Can I calculate circumference from diameter instead of radius?
Yes. Since the diameter is twice the radius (d = 2r), you can use C = pid. If you have the diameter, simply divide it by 2 to get the radius and use this calculator.
What units does this calculator support?
You can enter the radius in any unit (centimeters, meters, inches, feet, etc.) and the circumference will be returned in the same unit. The calculator performs pure mathematical computation without unit conversion.
Is the circle length calculator free to use?
Yes, all calculators on Calculy, including the Circle Length calculator, are completely free to use with no registration or hidden charges.
Can I share my calculation results?
Yes. After calculating, the radius value is saved in the URL. You can copy the page URL to share the exact calculation with others.
What is the value of pi used in this calculator?
This calculator uses JavaScript's built-in Math.PI constant, which provides approximately 15 decimal digits of precision (3.141592653589793).
How is circumference used in real life?
Circumference calculations are used in many real-world applications including determining the length of material needed to go around a pipe or wheel, calculating distances traveled by wheels and tires, designing circular tracks and rings, and solving geometry problems in construction and engineering.