The formula for the circumference of a circle is:

C=2πrC=2\pi rC=2πr

where:

• CCC is the circumference
• π\pi π (pi) is approximately 3.14159
• rrr is the radius of the circle

Alternatively, if you know the diameter ddd (which is twice the radius), the formula is:

C=πdC=\pi dC=πd

Let me know if you'd like an explanation or examples!