A family of Microsoft word processing software products for creating web, email, and print documents.
The short answer is that you can't. Tabs in Word documents are not measured in 'spaces' but distance. This is attributable to the almost universal use of proportional fonts. Also you need to take into consideration the font size and type. Seven 'spaces 'at 12 points will be somewhat less than seven 'spaces' at 16 points. Different fonts also have different widths at the same point size. So the question you need to ask yourself is how wide is a 'space'.