Please be more specific. See Rule #2.

Rich Text

Count Characters

You really can't reliably limit the number of lines in a rich text box when the text wraps automatically. Line wrapping depends on several factors like the font, font size, control width, and formatting, so the actual number of displayed lines can change.

The only time you can accurately count lines is if the user inserts manual line breaks (pressing Enter). In that case you could count those breaks, but with normal word wrapping Access decides where the lines fall. Because of that, the practical approach is usually to limit the number of characters instead, as Alex suggested, rather than trying to control the number of visible lines.

Thank you all for your responses! I decided to move the rich text box on my report to where it can grow and shrink.
Have a great day all!

Yeah if all you're looking for is good clean display then that's best. You could even embed the report inside of a form if you want.