This was known to be an underestimate as US planning did not take into effect the thermal effects of nuclear weapons due to a degree of variability from cloud cover etc. So probably about a billion would have died - then there is the effect of Soviet weapons...
I can recommend Daniel Ellsberg's book on the topic:
https://www.historytoday.com/reviews/confessions-nuclear-war...
https://en.wikipedia.org/wiki/M._V._Ramana
See for example:
"Bombing Bombay? Effects of Nuclear Weapons and a Case Study of a Hypothetical Explosion", 1999 International Physicians for the Prevention of Nuclear War (IPPNW)
https://www.ippnw.org/wp-content/uploads/2020/07/Bombing-Bom...
"Costing plutonium: economics of reprocessing in India", M.V. Ramana, J.Y. Suchitra, 2007
https://www.geocities.ws/m_v_ramana/nucleararticles/IJGEI_Vo...
"India, Pakistan and the Bomb", Scientific American, 2001
https://www.bing.com/videos/riverview/relatedvideo?q=google....
ben_w: "You're taking a comic book plot device as evidence?"
I was telling a story about my early life! Get a grip! It was a lead-in to a)the Soviet doomsday device which may have been real and may still be around and b)to my early fright at the nasty side-effects of nuclear weapons.
ben_wL "The former easily wipes out a city; the latter messes up a building."
Indeed an understatement! The Chernobyl reactor is an accidental "dirty bomb". It FUed quite a large area: people don't do much picnicking in the Chernobyl Exclusion Zone:
https://en.wikipedia.org/wiki/Chernobyl_exclusion_zone.
Spare me talking about how large the Chernobyl reactor and how heavy its fuel rods are, etc. Fissionable material and fission by-products are generally toxic: spreading it around is devastating and difficult to correct. And the Iranians have lots of that kind of crap.
https://babel.hathitrust.org/cgi/pt?id=uc1.31822013222641&se...
--- start quote ---
/* From Department of the Army's authoritative study: "Effects of
Nuclear Weapons", footnote 3 to section 1.45, available at:
http://www.fourmilab.ch/etexts/www/effects/
"The majority of the experimental and theoretical values of the
explosive energy released by TNT range from 900 to 1,100 calories per
gram. At one time, there was some uncertainty as to whether the term
"kiloton" of TNT referred to a short kiloton (2 x 10^6 pounds), a
metric kiloton (2.205 x 10^6 pounds), or a long kiloton (2.24 x 10^6
pounds). In order to avoid ambiguity, it was agreed that the term
"kiloton" would refer to the release of 10^12 calories of explosive
energy. This is equivalent to 1 short kiloton of TNT if the energy
release is 1,102 calories per gram or to 1 long kiloton if the energy
is 984 calories per gram of TNT."
So, evidently they don't quite specify which ton is required...
--- end quote ---And it goes on