The website I use is librarything.com
If I can’t find a specific book on my local library’s website, I type it into librarything and 99 times out of 100 it pops right up. Click on the title, scroll to the bottom of the page, and it’ll tell you exactly where it’s shelved.
Example: Miracle in the Andes (the plane crash book)

982.6 - history and geography - South America - Argentina
Example: What If? by Randall Munroe

502.07 - science and math - science - miscellany
Very useful! I also love browsing their MDS database (they use the Melvil Decimal System, which is functionally identical to the copyrighted and trademarked Dewey Decimal Classification system; both are named for creator Melvil Dewey)
Click on a category, 0 through 9, and it will open ten more subcategories below it. Keep clicking to go deeper and deeper. I have a few memorized; 599 is for mammals, 306 is for culture and institutions, 796 is more most sports.

7xx: arts and recreation
79x: recreation, sports, and performing arts
796: athletic and outdoor sports and games
796.8: combat sports
796.86: fencing
At the bottom of this page they’ll list every book that is classified under a given number, in case you’re looking for recommendations with no specific titles in mind.






