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.