How many trees are saved by using recycled paper?

Some typical calculations

*1 ton of uncoated virgin (non-recycled) printing and office paper uses 24 trees
*1 ton of 100% virgin (non-recycled) newsprint uses 12 trees
*A "pallet" of copier paper (20-lb. sheet weight, or 20#) contains 40 cartons and weighs 1 ton.

Therefore,
*1 carton (10 reams) of 100% virgin copier paper uses .6 trees
*1 tree makes 16.67 reams of copy paper or 8,333.3 sheets
*1 ream (500 sheets) uses 6% of a tree (and those add up quickly!)
*1 ton of coated, higher-end virgin magazine paper (used for magazines like National Geographic and many others) uses a little more than 15 trees (15.36)
*1 ton of coated, lower-end virgin magazine paper (used for newsmagazines and most catalogs) uses nearly 8 trees (7.68)

How do you calculate how many trees are saved by using recycled paper?

(1) Multiply the number of trees needed to make a ton of the kind of paper you're talking about (groundwood or freesheet), then
(2) multiply by the percent recycled content in the paper.

For example,
1 ton (40 cartons) of 30% postconsumer content copier paper saves 7.2 trees
1 ton of 50% postconsumer content copier paper saves 12 trees.

Source : http://www.conservatree.org/learn/EnviroIssues/TreeStats.shtml