Circumference Calculator
Circumference and diameter of a circle from its radius.
Worth Knowing
Circumference is the distance around a circle, equal to π times the diameter, and it's where the constant π was first encountered historically — as the stubborn ratio that no fraction quite captures. This tool derives both circumference and diameter from the radius. A pleasingly counterintuitive fact hides here: adding just one meter to a rope wrapped around the entire Earth would lift it about 16 cm off the ground everywhere, because circumference grows in simple proportion to radius.
How to Use
- Enter Radius into the Circumference Calculator above.
- Your result appears instantly as you type — there's no submit button or page reload.