A reader writes to demand:

Setting everything according to the various suggestions for Word to lay out my pages for writing a book, I find it impossible to get 25 lines on an 8½ by 11 when double spaced. Explain.

"Explain"? That's a rather imperious imperative sentence, but I'll do my psychic best to satisfy your command without your Word document in front of me for reference.

I'll summarize what I assume your problem is, though I've covered this issue in much greater detail elsewhere. But let me preface my summary by emphasizing that the number of lines per page probably doesn't even matter. As I try repeatedly to make clear, formatting your manuscript is about following general guidelines, not about breaking out your protractor and slide rule. It's an art, not a science. It's cooking, not baking. As long as your formatting falls in the general neighborhood of correctness, you'll be fine. Don't get so caught up in refining the finest details of your formatting that it bogs you down and distracts you from what's most important: writing the best novel you can.

That said, the issue that's reducing the number of lines you can fit on a page is probably related to line height (the amount of vertical space that each line takes up on the page). By default, Microsoft Word sets a line height that's a little greater than the standard for 12-point type. This results in fewer lines per page. If you're getting 23 or 24 lines per page, I wouldn't worry too much about. If you're getting even fewer than that, you might be doing something else wrong, like more-than-double-spacing your lines or using a text style that puts extra space between paragraphs.

If you're determined to make things precise, though, please see my fuller explanation of line height in the blog post I referenced above, "How line height relates to word count."