Length x Breadth ÷ 18.5 = persons capacity
Now this becomes U.S. Law on December 01, 2011, however if you want to check that your boat capacity plate and your Load and Capacity Certificate will remain unchanged use the 185 lbs. One excurscion boat just inspected in the Florida Keys was certified for 100 persons, under the new formula that will be reduced to 86 persons. Being a rather serious reduction NAUTICAL LOG checked with a well known Instructor and he was kind enough to get back straight away confirming he uses 185 lbs.
Make sure always to wear your lifejackets regardless of the capacity and the number of persons actually on board. Safe boating is no accident.
Please remember the seafarers held captive by pirates off Somalia - let us work with India to free them.