A weight additive is a tariff charge for certain larger shipment items which have a density so low that the space they occupy in the van is absurdly incommensurate with their weight. Examples of shipment items with a weight additive are canoes, kayaks, airplanes, horse buggies, and some boats and trailers. To compensate for this space/weight inequity, an average weight of 7 lbs. per cubic foot will be added to the item. For example, a 16’ kayak has an actual weight of just 95 lbs. but has a volume of 54 cubic feet. A weight additive is used to calculate the average weight that should occupy 54 cubic feet. The salesperson will multiply 54 times 7 lbs./cubic foot to get the weight additive of 378 lbs. This weight additive is then added onto the calculated weight for the rest of the shipment.