The smallest font to use on a resume is 10.5 points. Even 10.5 may be too small because some fonts are simply bigger than others. If your font size is too small, the hiring manager will have trouble reading your resume.
Arial Narrow at 10.5 is the smallest font and font size combination that looks good on a resume. This font is specially designed to appear narrower than other fonts, so you can fit more information on the page.