When Ray Bradbury wrote Fahrenheit 451, he allegedly chose the title for the temperature that paper, particularly book paper, catches fire. The idea was that the firemen use flamethrowers to burn books, and the fire needed to be at least 451 degrees Fahrenheit to properly burn the paper. However, proper scientific testing shows that paper ignites in a much broader range, anywhere from 4-800 degrees Fahrenheit, depending on the quality and thickness of the paper. In fact, some papers don't ignite until 450 degrees Celsius, almost double 451 degrees Fahrenheit. It is more likely that Bradbury chose the title because it sounded good than based on research of paper temperatures; of course, because of the popularity of the novel, many sources reference that temperature as accurate without further research.
the temp at which paper burns or catches fire.
451 degrees Fahrenheit is the temperature at which books/paper burns. It is very symbolic for this book!