Working with Document Files
In the United States, Word uses inches as the default unit of measurement. This means that in any input field that calls for a measurement (the one for left margin size, for example), you can just type a number; you don’t have to specify the unit of measurement. But what do you do if you want to use a unit of measurement other than the default? Do this:
Type the number in the input field, as always.
Without adding a space, type "in" for inches, "cm" for centimeters, “mm” for millimeters, "pi" for picas, or "pt" for points.
So if you want a left margin that is, say, 5 centimeters wide, you would enter “5cm” in the Left box on the Margins tab of the Page Setup dialog box.