Never thought I'd do a rule for d20, but Pathfinder 2 has taken an identity stance I can respect so I'm willing to look into it a little deeper. So I'm reading the bulk section of Pathfinder Second Edition, and I noticed:
1000 coins is 1 bulk and 1 bulk is 5-10 lbs. This was confusing to me because of previous editions being 50 coins per pound, a bulk should be 20 pounds. Also with a medium sized creature being 6 bulk, that's only 60 lbs. at 10 per bulk. I noticed that making Medium Creatures bulk 8-10 keeping small creatures at 2-3, and having 1 bulk correspond to 20 lbs fixes all of these issues for medium and small creatures. Likewise, a large creature could be 12-15 Bulk (240-300 lbs), a huge creature 25-30 bulk, and so on. This does not obey the square cube law but it fits closer to what actual d20 creatures seem to want to weigh, so it works.
Also, side note: There is some text about how an object's bulk is somewhat affected by its awkwardness more than its actual weight, and generally I'm willing to concede the point that a longsword is only a couple pounds, and other such concessions and not change how the rule works overall unless something glaringly annoying comes up.
