Estimating Postage

So we're sending a letter to Liz's brother in New Jersey, and I want to know whether I'll need extra postage. While Liz's part of the letter is written on a small, light sheet of stationery paper, my part is a four-page printed dissertation on Light and Knowledge and its role in our eternal progression. I know that the printing paper we're using right now is heavier than normal (we were lazy and bought it while we were shopping at Costco, and we had a choice between 800 sheets of heavy paper and a whole box of normal), so I set out on a quest to figure out about how much this letter will weigh.

First I looked at the packaging on our printing paper and found the "24 lb" marking. From my time spent working at Office Depot, I knew that this was a way of describing the paper's density, however, and not the weight of the ream. Some Internet research revealed that this weight refers to a ream (defined as 500 sheets) of "standard size" paper, which is not the 8 1/2"x11" that you might think, but rather 17"x22", which gets cut down to make four sheets of normal printer paper. So to calculate the weight of one sheet, we need to know:

1. There are 24 lbs of standard-sized paper in a ream.
2. There are 500 sheets of paper in a ream.
   
3. There are 4 sheets of letter-sized paper for each 1 sheet of standard-sized paper
4. There are 16 ounces per pound.
   

So (24 lbs/500 standard)*(1 standard/4 letter)*(16 oz/lb) = 0.192 ounces.

I figure Liz's letter and the envelope weigh less combined than one more sheet of printing paper, so just to be safe, I estimated about 5 sheets' worth, or 0.96 ounces at the most. Being under one ounce, it qualifies for a standard 42-cent stamp. Tah-dah!

Update

We ended up buying this kitchen scale, which has been extremely useful for measuring out ingredients in recipes and such. We also use it as a postage scale, which is much easier than doing the math each time.