What is the smallest and largest font size available in font size tool on formatting toolbar in Microsoft Word?

8 to 96 depending on what program you are using.

On the toolbar, the user is restricted to font sizes ranging from 8 to 72. However, there is an easy way of finding fonts smaller and larger than those in this range. Word actaully supports font size between 1 and 1638. You will have to access it through the Fonts dialog box.

Once there, you will find that the largest font size (at least, in Word 2007) is 1638 points. For practical reasons, the more usual font sizes are offered on the toolbar, but not all the range I´ve listed here-