The LAW of Total Tricks (LOTT) is a bidding guideline developed by Jean-Rene Vernes. It helps you to decide how high to compete, using this approximation:
With 8 partnership trumps, bid to the 2-level.
With 9 trumps--3 level.
With 10 trumps--4 level.
(This assumes there is no game or slam interest).
The "LAW" states that on most bridge deals the total number of trumps is approximately equal to the total number of tricks.
There are 3 articles on this website with more details, as well as a brief description of 3 books by Larry Cohen on the LAW:
BOOKS
To Bid or Not to Bid (the classic bestseller on the LAW of Total Tricks)
Following the LAW (sequel to above)
Introduction to the LAW (simplified "lite" version)
ARTICLES
Responding to Preempts using the LAW
Responding to 1-Major using the LAW
Balancing using the LAW
Original Vernes article courtesy of Bridge World Magazine