The actual weight in pounds of 500 sheets of paper (a ream) is the ream weight. If you know the actual size of the sheets of paper, its basis weight, and its basic size then you can calculate the ream weight without putting the ream of paper on a scale.
While this isn't information you absolutely need to know to do desktop publishing, it can be helpful if you need to calculate weight to estimate shipping costs, etc.
To calculate the ream weight use this formula:
actual sheet size x basis weight / basic size
Using this formula, the ream weight of 500 sheets (one ream) of tabloid size (11x17) 24lb book paper would be:
(11x17) x 24 / 25x38 = about 4.72 pounds
The basic size of book paper is 25x38.
Ream weight is not the same as basis weight (unless the the sheet size and the basic size happen to be the same).
If you picked up a ream of letter size (8.5x11) printer paper at the office supply store and it said it was 20lb paper, that doesn't mean the ream weighs 20 pounds. 20lb is the basis weight of the paper. Using the above formula, that ream of 20lb paper (bond paper has a basic size of 17x22) actually weighs around 5 pounds, not 20:
(8.5x11) x 20 / 17x22 = 5 pounds
Paper Calculators:
- International Paper: How to Calculate Ream Weights (note the rounding rules). I'm not entirely sure how it is applying its rounding rules. The calculation of 4.72 pounds in the first example, above, actually comes out to 4.7242 on my desktop calculator but 4.7 on the IP calculator. The second example of 5 pounds (per my desktop calculator) is 5.5 pounds on the IP calculator.
- Case Paper: M-Weight Calculator M-Weight is 1000 sheets so cut the answer in half for your ream weight.
- Sabin Robins: M-Weight Again, cut the answer in half for your ream weight.
