Paper is a peculiar business, in the US, anyway. The rest of the world uses the Metric System, which uses thickness and weight, and not the kind of paper, as nomenclature. We have a different name for each kind of paper, and a rough system of classifying different papers according to the weight of a 500-sheet ream. Of course, they make it weirder by using different size paper to determine the weight for each kind, i.e. typing or bond paper is based on the weights of 500 sheets of 17"x22", while index is based on the weights of 500 sheets of 25 1/2"x30 1/2". Then, different manufacturers follow different specs.
Originally Posted by T-Rex
The only way to know for sure is to measure with calipers.
A good day of flying rockets is one where you get all the parts back.