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Apr 1, 1996 12:00 AM
Almost all paper is sold by the pound, not by the sheet. Therefore, knowing the number of sheets does not tell us the cost of the paper. First, we must determine how many pounds of paper a certain number of sheets will make. Then, we ask paper merchants the cost per pound for that amount.
The basis weight of the paper is the starting point for calculating pounds, while basis size is the starting point for basis weight. For example, the basis size for bond paper is 17 x 22 inches. Don't ask why. It makes as much sense to ask why there are 16 ounces in a pound or 12 inches in a foot. However, it does happen to be a practical size because there is no waste when cutting four 8 1/2 x 11-inch letterheads out of 17 x 22 inches.
By definition, if a ream (500 sheets) of 17 x 22-inch bond paper weighs 20 lbs., the basis weight of the paper is 20 lbs. If it weighs 24 lbs., the basis weight is 24 lbs.
The basis size for book paper, commonly called coated, offset or text paper, is 25 x 38 inches. The basis size for cover stock is 20 x 26 inches. If a ream of 20 x 26-inch coated cover weighs 80 lbs., it is 80-lb. coated cover. Therefore, 80-lb. cover is thicker and approximately twice as heavy as 80-lb. coated book paper. A 20 x 26-inch sheet, which is about half the size of the 25 x 38-inch sheet, weighs as much as the larger sheet.
If all the information we have is that a ream weighs 80 lbs., it is difficult to determine what 1,765 sheets weigh. We would have to perform the following tedious calculation: 1765/500 = 3.53 reams x 80 lbs. per ream = 282.4 lbs. Instead, we convert ream weights to pounds per thousand sheets. If the above 80-lb. paper is 25 x 38 inches (the basis size), then 1,000 sheets (a ream of 500 sheets x 2) weighs 160 lbs.
The 160 lbs. is the M Wt., the weight of 1,000 sheets of a particular basis size and basis weight. Now we can work with the decimal system to calculate the weight, which is much simpler: 1.765 x 160 = 282.4 lbs.
If the paper size is smaller, the M Wt. is lower, and if the paper size is larger, the M Wt. is higher. Thus, 19 x 25 inches is 80M and 38 x 50 inches is 320M. All we did was halve or double the original 160M.
However, what about all the other sizes, such as 23 x 35 inches? Unless we have extraordinary memories, we have to use a lookup table in a paper catalog. The table shows the M Wt. of 23 x 35-inch 80-lb. book paper is 136. In addition, we can see all the M Weights of the standard weights and sizes in which paper is made.
Computer-assisted estimating makes the whole process much easier. When the software program is installed, it asks for the number of square inches of the basis size of each kind of paper the company uses. The answer for book paper would be 950 sq. in. (25 x 38 inches). For cover paper, it would be 520 sq. in. (20 x 26 inches). Then, knowing what kind of paper is used in a particular estimate, the program applies the formula shown in the adjacent chart. Then, we can check the 135.58 or 136 amount in the catalog to verify it.
The process is easier if the estimating program is linked to the company's paper inventory. In that case, the estimator simply keys in the inventory lot number. Immediately all the vital information about the paper pops up, including the number of pounds, cost per pound and total cost.
The same formula, applied manually or by computer, works equally well if the paper is an unusual size. This calculation is especially useful when determining the cost of mill makes. If we could use a 21 x 33-inch sheet instead of 23 x 35-inch, and need 5,000 lbs. or more, most mills will sell the paper at no additional cost per pound. The M Wt., after the mill rounds it up to the next highest number, would be 118, a savings of 18 lbs. for every thousand sheets.
width x length x (basis weight x 2)/width x length of basis size
For the 23 x 35-inch 80-lb. sheet, the calculation would be:
23 x 35 (80 x 2)/25 x 38 = 128,800/950 = 136
DON MERIT, Contributing editor. Merit is a production management and estimating consultant based in New York City