Manuscript pages equals how many pages in a novel?

Used? Word count is used. Page count is pretty much meaningless, because it can be totally change by a change in formatting.

Trade paperback or mass market? Like you said, it varies depending on page layout, typesetting, font size, etc.

But let's keep things simple. Let's consider it's standard ms. format. It's about 250 words per page (give and take, of course, depending on how much white space you have). A trade paperback probably has 350 words per page. So you can do the Math:

10 x 250 = 2500 ~= 7 x 350

So, 10 standard ms. pages would probably translate to about 7 trade PB pages.

As many as the book's designer wants it to be.

The standard is word count, not page count. A length of 100,000 words in a manuscript will be instantly understood by an agent or editor. So will 400,000 words.

caw

My dad told me that one computer page equaled 1 1/3 book pages, but I actually don't think he knows.