to everyone who responds with "it's proportional to square footage": nobody flies planes configured for business class only. "if the moon was made of cheese we couldn't mine 3He from it" but in reality it isn't so why should I accept this assumption?
i stand corrected, your ass does weigh more in a first class seat (if you add the weight of the seat in) https://ruby.social/@halfbyte/117118864402458450
interestingly, the infographic above doesn't look like a very close match to IATA class factors (below; which i didn't know about) but is a pretty close match to "going from economy to business class seat effectively doubles passenger weight"