Some authors waste a huge amount of energy as they draft a chapter worrying about how many pages long it's gotten to be. I'm one of those dopes. Since all my chapters are in one file, the page count at the bottom of the screen doesn't help. But there is another way to get Word to tell me. This "tip" is for equally misguided souls who have some experience with Word.
This trick works well in combination with chapter titles assigned Heading 1 and Document View turned on, but those aren't essential. You do need a section break after each chapter.
Put your cursor at the end of the chapter title. Space. Now insert the field SectionPages. Here's how.
Word 2007 for Vista: Go to the Insert tab. Find Quick Parts/ Field. Find SectionBreaks and click on it. Click OK.
Word 2003 for Windows XP: Insert/ Field/ SectionPages. Click on it, click OK.
Word 2004 for Macs: Insert/ Field. For Category, select Numbering. The Field name is SectionPages.
Word will drop a number where your cursor was. (This really is a field with programming behind it, not a simple digit.) To speed up adding it to each chapter title, copy the number/field you inserted and paste it in the same place for each chapter title. You will see the number in Document View. Drag the Doc View window wider if necessary.
BUT this section (chapter) page count will be wrong. You must update the fields. Use Ctrl + a (Command + a for Macs) to highlight the entire document. Now press F9 in the top row of your keyboard to "update fields". All the numbers will now be correct, and you will know how long each chapter is. (I had some trouble testing this with a Mac--let me know if it works for you.)
Word will update the fields every time you re-open the document. More important to neurotic writers, you can highlight the document and press F9 whenever you start to worry that the chapter is too short, too long, or full of porridge.
Remember to get rid of the fields before you submit your ms. An easy way is to use Outline View set to Level 1. At each chapter title, delete the field.
Authors are such worriers. Just back up your files and get on with it!