511 (disambiguation)

511 may refer to:


 * The year 511 AD of the Common Era
 * The year 511 BC before the Common Era
 * The number 511 (number)
 * The telephone number 5‒1‒1, used for transportation information in many regions of Canada and the United States of America
 * 511 keV, the energy of each of the two photons created when a positron and an electron annihilate