Calculating the weight of paper requires the Basis Weight or M-Weight of the paper.


The M-Weight (MWT) is the actual weight of 1000 sheets of a particular size.  If a sheet is cut in half, the MWT is also halved.

The basis weight (BWT) is the actual weight of 500 sheets (a ream) of the basic sheet size. The basic sheet size depends on the grade of paper.  If a sheet is cut in half, the BWT remains the same.


80# Text = 500 sheets of 25 x 38 will weigh 80 pounds

80# Cover = 500 sheets of 20 x 26 will weigh 80 pounds


Here is a listing of commonly used paper grades and their basic sheet sizes:

 

GradeBasic Size  Sq In (BSQ) 
 Board 22 x 28 616 
 Bond 17 x 22 374 
 Book 25 x 38 950 
 C1S/C2S Cover 24 x 36 864 
 Cover 20 x 26 520 
 Index 25.5 x 30.5 778 
 NCR 17 x 22 374 
 Newsprint 24 x 36 864 
 Offset 25 x 38 950 
 Opaque 25 x 38 950 
 Tag 22.5 x 28.5 642 
 Text 25 x 38 950 
 Vellum Bristol 22.5 x 28.5 642 
 Writing 17 x 22 374 

When the M-Weight (MWT), Basis Weight (BWT) and Sheet Size are known, the BSQ can be calculated using the following formula:

BSQ = ( 2 / (MWT/BWT) ) * Size
 
MWT = (BWT * Size * 2) / BSQ
 
BWT = (BSQ * MWT) / (Size * 2)

Note: Envelopes don't generally have a basic size.  For estimating purposes we recommend using 475 square inches.