How do you find out how many beneficial bacteria are in yogurt?  A commercial lab will analyze samples and report a certain number of CFUs, or Colony Forming Units per gram.  Colony Forming Unit denotes active bacteria as opposed to inactive or dead bacteria.  A single bacterium can divide and form a 'colony' of many bacteria. 

Getting yogurt analyzed is not something anyone or any company does frequently as the cost is prohibitive.  A single sample can cost $600.  Most yogurt companies do not put their CFU count on their packaging due to the count's inherent variability.  Every container of yogurt is not going to have the exact same amount of CFUs.  Due to labeling laws, a producer would be exposed to legal action if someone had a sample analyzed and the CFU count was not what was on the label.  Age, seasonal ambient temperature during processing, human process variations, temperature master culture stored at before inoculation, varying lactose content of the milk, shipping conditions, etc., can all affect the actual CFU content of a given sample of yogurt.

White Mountain Foods' most recent yogurt analysis reported 400 million CFU per gram of yogurt.   That's 90.8 billion per one cup serving.