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

See also

511th (disambiguation) 51 (disambiguation)