Can anyone give me a simple explanation of this method or a link to someplace where it's explained clearly enough to be useful?

I'm confused.
 

Word-count is not always helpful in determining just how many pages a story will take up (lots of dialogue "stretches" the page count) so different publishers may have their own approach to calculating pagecount (depending on binding method, etc, page count can actually be very important).

In general if you have any queries you should ask the specific publisher in question.
 

In the most basic average word count, 250 words per standard manuscript format page. This count is not likely to be appreciably different from actual publication real estate. As far as a writer is concerned, this is about all that's needed. Whoever at the publisher does an actual assessment will be the one whose count is relied upon. Any other assessment can vary up to 20% from the house estimate. Wordprocessor word counts are commonly low by 15 to 20%, too.

More detailed, count several typical lines for average number of words, multiply by average number of lines per page, times number of pages.

A more detailed count takes into account short lines, section breaks, chapter sinks, half-page opening and ending pages, etc.

In standard manuscript format, a line has 66 characters including word and sentence spaces. A page has 25 actual lines, including header. In standard written English an average word has 5 to 6 characters, so an average line count is 10 to 11 words, thus 250 words per page. A standard published page of a novel also averages 250 words.

[This message has been edited by extrinsic (edited April 06, 2009).]
 

Back in the olden days, when I relied on typewritten manuscripts, I used to take three pages, count every word on each page, divide by three, and multiply by the number of pages in the manuscript (counting the short first page and short last page as one.) For a very short MS, I counted the words on every page.

Back further, very early on in my career, I used a method recommended to me, where I count the words in one line, multiply by the number of lines on the page, then multiply by the number of pages. I was never happy with that---too many short lines, too much risk of unreliability.
 

http://www.sfwa.org/writing/wordcount.htm

Of course, any discussion on word counts is bound to get way out of control.

It's pretty simple, really.

A properly formatted MS page has about 250 words. So if you want to find your word count, multiply the number of pages by 250 and any half page by 125, then round to the nearest 100th.

The only exception to this is if you're figuring out the word count for a novel. Novels are so long that a general estimate is all that required. So just multiple the number of pages by 250 and round to the nearest 1000th.
 

I, too, use the 250 words per page to determine the length of my work. The trouble with the word count the computer comes up with is that it counts every single word. So the count can vary dramatically when done with the 250 words per page method. I've read several books on publishing that says most editors/agents prefer this method for word counts and never to use the count given by the computer.

[This message has been edited by Crystal Stevens (edited April 07, 2009).]
 

When I said that for half a page count 125 words, I was talking specifically about short stories. For example, if I have a story that ends with 8 lines on page 25, that's about 6,100 words...(24*250)+125 = 6,100 rounded to the nearest 100th.

For novels/books, you're absolutely right. Count every page, then round to the nearest 1,000th.

Sorry for the confusion.