The Modern Language Association (MLA), American Psychological Association (APA) and Chicago Manual of Style guides use a 12-point font size, unless the publication or university receiving the paper submission specifies otherwise. A 12-point font is considered the most readable size, and it is the standard across all of the writing disciplines.
Most standard style guides also indicate the preferred font face. In the vast majority of cases, the preferred font is Times New Roman, but other readable fonts that may be allowed include Arial and Calibri. Every style guide has its own directives on paper formatting, including the required margin size and whether a cover page or header is mandatory.