Pi to 39 digits … should be accurate enough for anybody.

Knowing pi to 39 decimal places would nearly suffice for computing the circumference of a circle enclosing the known universe with an error no greater than the nucleus of a hydrogen atom.

Dr. Neil Basescu, Madison, Wisconsin

http://www.straightdope.com/columns/read/818/how-do-scientists-go-about-calculating-pi-to-umpteen-decimal-places