thud factor
n. A characteristic of a book or magazine that measures its relative weight; whimsically, the "thud" a book or magazine makes when you drop it on a desk or table.
They are part of a growing breed: the obese magazine, publications so fat that if they were people, they might spend their time in a high school auditorium sweating to the oldies with Richard Simmons.

Toss them on a desk, and you'll hear what publishers like to refer to as 'the thud factor.' (The louder the thud! thunk! or boom! the better.)
—Alex Kuczynski, “A Little Light Reading, Anyone?,” The New York Times, April 11, 2000
1989 (earliest)
Andy Silverman, technical vice president of 88Open's San Jose (Calif.) Technical Center, said he's willing to play "thud factor" with any RISC vendor's book of ISVs (the 88Open Software Sourcebook comes in at 200 pages-plus) now that the group has signed up more than 200 companies.
—Loring Wirbel, “Other voices at Expo,” Electronic Engineering Times, October 30, 1989