The calculations are based on the following stats from Conservatree:
-1 ton of uncoated virgin (non-recycled) 20# printing and office paper uses 24 trees.
-1 ream of paper (500 sheets) uses 6% of a tree.
-1 tree makes 16.67 reams of copy paper or 8,333.3 sheets
-The trees that are being used to make the paper are a mix of 40 foot-tall hardwoods and softwoods, 6-8" in diameter.

Conserv A Tree:
www.conservatree.com: Claudia Thompson, in her book Recycled Papers: The Essential Guide (Cambridge, MA: MIT Press, 1992), reports on an estimate calculated by Tom Soder, then a graduate student in the Pulp and Paper Technology Program at the University of Maine. He calculated that, based on a mixture of softwoods and hardwoods 40 feet tall and 6-8 inches in diameter, it would take a rough average of 24 trees to produce a ton of printing and writing paper, using the kraft chemical (freesheet) pulping process. [URL:http://www.conservatree.com/learn/EnviroIssues/TreeStats.shtml]

Much of this data was collected from a great blog published by Tamara Krinsky, the
founder of Change the Margins, a blog aimed at getting Microsoft to change the default settings on their word doc margins. She believes this is one of the greatest wastes of paper around and something that is very easily fixable. Check out here blog at
www.changethemargins.com.