(For reference only – our prices are based per 100 pounds.) A base box is measured in terms of pounds per base box. (112 sheets 14″ x 20″) a unit peculiar to the tin plate industry and refers to thickness indirectly. This corresponds to an area of sheet totaling 31,360 square inches of any gage and is applied to tin plate weighing from 55 to 275 pounds per base box. To convert weight per base box to decimal thickness, multiply by .00011.