How do you know when to spell out numbers and when to use numerals?sixteen children vs 16 children In the 70's The house on 1st Avenue

Generally, we use the rules from either the Modern Language Association (MLA) or the American Psychological Association (APA) to guide us in this area.

The numbers from one to ten should be written out, and numbers from 11 to infinity are supposed to be in numeric form.  However, there are some exceptions.  One is that a sentence should not begin with a numerical representation of a number.  Here are correct and incorrect examples:

Eleven little pigs decided to leave home.  (Correct)

11 little pigs decided to leave home. (Incorrect)

Another exception involves the situation in which you have two numbers in a sentence, one being a number from one to ten and another being a number over ten.  If you follow the general rule, it looks inconsistent. In those cases, it is best to write out both numbers.

For years, such as "the 60's," either the written out form, the "Sixties," or the numerical form is fine.

For a street name, you need to find out what the municipal or post office version is and use that version.

I should also mention that there are other style guides that can control numbering conventions.  These include the Chicago Manual of Style, the Associated Press Style Guide, and the Bluebook, which attorneys use for formal legal writing.

Given all of the possible guides that dictate how numbers are used, the choice you make might depend upon your audience for writing. If you were writing for an English class, you would probably need MLA.  If you were writing for a psychology class, you would certainly use APA.  A journalist usually uses the Associated Press guidelines. but some newspapers, for example the New York Times, have their own style guides.  I am providing links to websites with information on APA and MLA, and I hope that is enough to get you started. Those of us who must do extensive writing usually end up purchasing the specific style guides because there are many little detailed requirements that differ from guide to guide.  Numbers are probably the easiest part of all this!

Good luck.