For this particular event, see https://losc.ligo.org/events/GW151226/, near the bottom of the page
"The amount of matter converted to energy in the atomic bomb dropped on Hiroshima was about 700 milligrams, less than one-third the mass of a U.S. dime."
(From http://discovermagazine.com/2010/jul-aug/24-numbers-nuclear-...)