The standard size (basic size) is not the same for all paper grades. The major paper grades such as bond or cover have their own standard sizes which determine the basis weight for that grade of paper regardless of the final cut size of the paper used or sold to consumers.
A ream of all purpose letter-size desktop printer paper may have a basis weight of 20lbs. but that doesn't mean that the ream of letter-size paper weighs 20lbs. The 20lbs is based on 500 17x22-inch sheets of that particular paper.
Because the basis weight is based on various basic sizes which differ among different types of paper, basis weight alone isn't sufficient for choosing a paper. 80lb text paper is not the same as 80lb cover, for instance. You'll need to know if you're talking about bond paper, cover paper, text paper, etc.
Basis Weight Charts
These various charts show different ways of looking at basic sizes and basis weight by paper grade or use.- The Paper Mill Store PDF: Calculating Basis Weight and Using Paper Grade Weight Charts
- Paper Weight and Size Charts at paper-paper.com
- Paper on Web has a big chart of Basis Weight of Some Papers that includes grammage, and caliper for comparison.
