According to the conversion tool at WordsToPages.com, there are approximately 450 words per page on a single-spaced document with standard margins and a 12-point Arial font. This estimated number of words is based on an academic essay with four paragraphs per page and no headings.
The total number of words and pages of a Microsoft Word document is typically displayed within the status bar at the lower left corner of the screen (e.g. Page: 1 of 1, Words: 116). If not found there, it may be obtained by right-clicking the status bar and selecting Word Count from the list of options.