Q. What is the portion I can use of a copyrighted work and it still fall under fair use?

Please see the bottom box of this link on the Copyright Guide for Reserves and E-Reserves information. 

Unfortunately and fortunately, there is no hard and fast percentage or portion rule that can help you determine what would be a Fair Use.

You may have heard of the 10% rule, or of using "only one chapter or article" from a publication, but these come from guidelines, not law, and have stuck around despite their flaws. A Fair Use can only be decided by a court, which you probably want to avoid, but it is important to note there are cases where using the entirety of work can be seen as a Fair Use, depending on the use. Though an educational use would likely weigh in your favor if you are faculty needing the portion for a class and using more than just the portion needed would weigh against your use, 10% is arbitrary. 

10% is also up for interpretation sometimes. For images, does it mean 10% as in size/scale/pixelation of an image, like a thumbnail version? Or only 10% of a section of a larger image? As you can see, 10% doesn't even translate well as a rule. 

What is more, if the “heart” or core essence a work is used, it may not be deemed a Fair Use, regardless of the percentage of the work that was used.

Fair Use is one of the exceptions to copyright law. To evaluate whether something is Fair Use you must weigh all of the four factors of Fair Use. Just because you think something is Fair Use doesn't mean TCC as your employer will! Please see our copyright policy on the TCC Library Copyright Guide.

On textbooks: 

If using an online textbook for a class you are teaching, the ability to download sections to share with your class may be disabled (also known as a form of DRM) or sharing access (such as a login) might go against the license/terms you have with the vendor or publisher, which would trump copyright exceptions in this case (in other words, it's a licensing issue, not a copyright issue). Please note the librarians do not have access to most department agreements with textbook publishers to know what is and isn't allowed with your specific course textbook. You might have to check with your department head or office. Depending on your need, circumvention for your use might even go against the DMCA. If you determine that your use of the copyrighted work does not fall within the Fair Use exception, you may always leave a print textbook or other material on reserve in the library for your students to read. Please contact the campus library where you would like the material to be reserved. More information about reserves and e-reserves can be found toward the bottom of this page of the Copyright Guide. 

A relevant video for faculty and staff at TCC:

"Yes, you can scan that textbook*" from ASERL on Vimeo.