What is the calculation for getting pi?

pi is defined to be the measure of the circumference of a circle divided by its diameter.

If you want a formula, you can use:  pi  =  4/1 - 4/3 + 4/5 - 4/7 + 4/9 - 4/11 + ...

(Keep this pattern going forever.)   However, this method is very s...l...o...w...

If you want faster formulas (but quite more complex), use Google ...

There are literally thousands of "algorithms" for computing Pi.

geno3141: That infinite series WILL NOT give you accurate digits of Pi!!!!!!!. Please see this link

https://en.wikipedia.org/wiki/Leibniz_formula_for_%CF%80  

Under the section of: "Unusual Behavior".