Wondering why your agent of choice asks for a word count instead of the number of pages?
Page length can vary widely on the publishing end. If the font is a bit smaller or the margins are a bit wider, or the page size is a bit larger, it will result in a completely different page count.
If the agents and editors (the publishing industry as a whole) used page numbers, the number would constantly change depending on the stage (from the writer's computer to a bookstore's shelf). Word count, however, stays pretty much the same.
Throughout the years, word count has shifted back and forth, especially with genre fiction. There might be a few outliers (Agatha Christie, JK Rowling...) who have much higher or much lower word count than their peers. But, unless you have an absolute slam dunk of a book, you'll spook an industry that has become increasingly risk adverse.
Even if you opt for the self publishing route, statistics show readers give better reviews (and return for more) with the following word counts.
Novella: 40,000 or less
General Fiction: roughly 80,000
Science Fiction & Fantasy: 115,000 or less
Mystery: 75,000 to 80,000
Young Adult: roughly 60,000