Calculating a Boat's Capacity
If you cannot find any other information about your boat’s capacity, use the following rule of thumb to estimate the number of persons (150 lbs. each, on average) the boat can carry safely in good weather conditions. The formula is useful for canoes but does not work for kayaks.
Number of people = boat length (ft.) × boat width (ft.) ÷ 15
For example, for a canoe 16 feet long by 3 feet wide, the number of persons is 16 times 3 (or 48) divided by 15, which equals three 150-lb. persons (or a total person weight of 3 × 150, or 450 lbs.).