Basic Paper Sizes (BSQ)

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:
 
Grade Basic 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.