looks ok except pie is 3.141592 -more accurate than value given on the site and if u want to be perfect:

http://www.geom.uiuc.edu/~huberty/math5337/gr...igits.html

do you have one or more values?

diameter is twice the radius,
Pi is defined as the ratio of a circle's circumference C to its diameter d:

pi = C/D ,which is 3.141592 etc

C= pi x d

d=2 x radius