Is $22/7$ equal to the $\pi$ constant? 
Possible Duplicate:
Simple numerical methods for calculating the digits of Pi
How the letter 'pi' came in mathematics? 

When I calculate the value of $22/7$ on a calculator, I get a number that is different from the constant $\pi$.

Question: How is the $\pi$ constant calculated? 
  (The simple answer, not the Wikipedia calculus answer.)


As already mentioned by others, $\pi \neq 22/7$. To answer your question, how to compute digits of $\pi$, $\pi$ can be obtained as a limit of sequence of numbers which can be computed to great accuracy.
For instance, the Madhava-Leibniz formula can be used to compute the digits of $\pi$. In fact, it was one of the first ways to compute the digits of $\pi$. $$\pi = 4 \times \left(1 - \frac13 + \frac15 - \frac17 + \frac19 - \cdots \right)$$ If we truncate the above series at $n$-terms, i.e. if we denote $$x_n = 4 \times \left(1 - \frac13 + \frac15 - \frac17 + \frac19 - \cdots + (-1)^{n} \frac1{2n+1}\right)$$ error analysis will give you that the $|| x_n - \pi|| \leq \left( \frac2n \right)$. The convergence of this series is hence slow. If you want an accuracy upto $2$ digits, you need to take of the order of $200$ terms.
There are other well-known series/ products which converge to $\pi$.
