In CHS, B-29's have a load of 14,000 lbs. Japan is extended range from the Marianas, meaning that the effective load delivered pr. B-29 will be 7,000 lbs, or 58.5% of the historic average.
This is for technical reasons. You won't find this in reference books, but it is in histories. The problem was that US strategic bombing doctrine was a failure, and a theater specific failure. Daylight bombing was never quite what its advocates said it would be - but it kind of sort of worked in ETO. This was not possible in Japan - where 85% of the time targets were "socked in" - making visual bombing impractical. Gen Curtis LeMay became something like Chief of Operations of the appropriate air force and changed the rules. [He did so in violation of both law and orders from the JCS too - not something we tend to stress when speaking of war crimes. War crimes tribunals had NO authority over Allied war crimes - and we put Germans in prison for bombing Rotterdam on a much smaller scale than the bombing we did. We killed more Japanese civilians in the last eight months of PTO operations than Japan lost soldiers in 10 full years of war - 1935 to 1945. And that using OUR watered down statistics - 800,000. We almost certainly killed that many in just two days in the Tokyo raids in April 1945 - according to an American demographer I met in Tokyo studying population records.] Anyway, LeMay's idea was to firebomb - literally "to burn out every square mile of Japanese urban area" and he said the war would magically end the day the last square mile was burned (about 1 Nov).
To achieve this, the B-29 went in low, stripped of all defensive armament, and overloaded - they each really DID carry more than the paper stats say - something like Kamakaze loads were bigger than the max loads for the same planes. Both my parents served in bombers in USAAC, and I grew up next to the home of the official US Army historian of the war, with access to his files. I sort of cut my teeth on this stuff.