Q. What margins should I use?
A. One-inch margins all around is a typical default setting for manuscripts, whether you’re using 8.5 × 11–inch or A4 paper, except for any headers and footers, which are typically half an inch from the edge of the page. One inch is equivalent to 2.54 centimeters or 6 picas; half an inch would be 1.27 cm or 3 picas. That’s what a US English installation of MS Word shows when the measurement options under File > Options > Advanced > Display are changed from inches to centimeters or picas, respectively.
These default settings are fine to use in most cases. But if you’re writing for a publisher, consult your publisher’s guidelines (and see “How to Format a Novel for Submission” at CMOS Shop Talk). If you’re writing a dissertation or thesis or other type of paper for school, consult our paper-formatting tip sheets, which are modeled on the examples in Kate L. Turabian’s A Manual for Writers of Research Papers, Theses, and Dissertations (9th ed.).