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A unit of explosive energy equal to that of one million metric tons of TNT.

meg′a·ton′nage (-tŭn′ĭj) n.
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.


the explosive power of a nuclear weapon, or the total explosive power of multiple nuclear weapons, expressed in megatons
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014
References in periodicals archive ?
The newly disclosed and declassified information details the U.S.'s nuclear disarmament and efforts to reduce its nuclear weapons total between 1962 and last year, as well as details on previous placement of weapons near Japan, the names of and megatonnage of older weapons, and even numbers on weapons stationed abroad.
From the metric of "equivalent megatonnage," which linearized the total destructiveness of superpower nuclear arsenals on the basis of the total area their warheads could theoretically expose to a certain blast overpressure, to the more sophisticated "counterforce potential" that incorporated accuracy to estimate an arsenal's total ability to hold hardened targets such as ICBM silos at risk, to full strategic exchange models that aimed to estimate how many weapons would be available to retaliate after a preemptive strike, analysts generally assumed that nuclear war could be reduced to measures of radii and area.
Conway Morris, "The Cambrian 'Explosion': Slow-Fuse or Megatonnage?," Proceedings of the National Academy of Science 97, no.
In terms of total megatonnage, the advantage certainly lies with the other side.