To calculate needed trailer capacity, calculate the total weight including the boat, engine(s), a full fuel tank (approximately 7lbs per gallon, full water & waste tanks (if included), and your personal gear.
Outboard boat dry weights DO NOT include the weight of the motor[s] whereas Inboard boats and I/Os do include the weight of the motor[s]. A good rule of thumb is to use 10% of the boat, motor, and liquid weights for personal gear. Select a trailer with the next highest capacity rating. If you intent to carry additional gear or luggage in the boat over long distances, consider the weight of these items, too.
also see Venture's web page on this topic: