One of my colleagues has in her e-mail signature "Please think of the environment before printing this. 1 ton of paper = 17 trees". That's all fine and good. But how many sheets of paper do you get from a tree ? Indeed is there a standard for the size of a tree ? Since we're dealing with approximations I'm going to treat tons and tonnes as equal. 80 gsm paper is easy for the arithmetic. 1 SQ metre (A0 size) weighs 80 grams, so A1 size = 40g, A2 = 20g, A3=10g and A4 size is 5g. 200 sheets weigh 1Kg and 1 tonne, is 200,000 sheets. If 17 trees is 1 tonne, 1 tree is 0.06 tones, or 12,000 sheets. So 12 sheets = 1 millitree. WikiPedia says 24 sheets make a quire, which is a nice round 2 millitrees.
You have to wonder how many of these units an army uses in a year 🙂