Determining whether your use of an item falls within Fair Use guidelines can be more problematic than you might think. Luckily, there's a tool that can help with that -- Fair Use Evaluator, from the American Library Association's Office for Information Technology Policy. By providing information about an article and your intended use of that item, the Fair Use Evaluator can provide you with an idea of where on the spectrum from "Fair" to "Infringing" that your use may fall.
The makers of the Fair Use Evaluator are careful to note that this tool is not intended to provide you with legal advice and point out that only "a court of law can definitively rule whether a use is fair or unfair." However, the Fair Use Evaluator does provide you with information that can help, such as a time-stamped pdf document showing your use of the evaluator and the criteria you used to reach your decision about whether your use of a document falls within Fair Use guidelines. Check it out. Try it with the Exceptions for Instructor eTool if you are a faculty member.