Tin was shipped from England to the states in boxes made of elm wood.  There were 225 sheets in a box of 10x14 or 112 in a box of "doubles" 20x14.  The footage of a basis is 35,100 sq inches for singles and 62,720 sq inches for doubles. 

The grade of tinplate was determined by the manufacturing process.  Coke or Charcoal was used in the smelting process.  Charcoal was for the finer grade.  

IC and IX are thickness of sheet.  Thickness is often refered to by gauge.  Such as 28 gauge or 30 gauge (30 being thiner)

The modern commercial manufactured hot dip tin is .00018 inch thick. This equates to 3 pound coating.  That means 3 pounds of tin would cover 225 sheets.  A redipped or vat dipped sheet may be as much as 10 pound coating.