How do you find cicumference with only knowing the radius?

To find the circumference of a circle you multiply pi, usually rounded to 3.12, by the radius. The formula for the circumference of a circle is 2*pi*radius.

So double your radius, then multiply by pi, which is approximately 3.14159265

So if I had a circle of radius 2, my circumference would be 2*3.14*2 = 12.56

Good Luck!