on Jane Friedman site:

Note from Jane: Today’s post is excerpted from the book Cover to Cover by Andrew Watson, a comprehensive guide to self-publishing a print book or ebook, mainly for those in Australia. However, the book printing information below is applicable to any author who wants to invest in a print run for their book.

Keep in mind that, due to the pandemic (and other factors), the market right now is very tight for paper and printing, with long lead times and increased pricing. Plan far in advance if you have a specific release date in mind.

Choosing the right materials for your book, and the right printer, is more important than you might think. They will not only affect its physical appearance but also influence a potential customer’s perception of value for money. You’ll also need to know exactly what to ask for when requesting and receiving quotes from a printer whether near you or overseas.

Everything below should be regarded as general guidance only. There will, inevitably, be variations depending on what is available at the time and the technical preferences of your nominated printer. When in doubt, always get a sample.

Depending on where your printer is based, they may express a paper’s weight in pounds per ream (#), grams per square meter (gsm), or points (pt). In this article, we’ve provided US and rest-of-world equivalents.

Note also that papers manufactured for different purposes utilize different systems of measurement. For example, a 100# cover stock is much heavier and more rigid than a 100# text stock.