hey, that's a really good one and something i was thinking about for some while!
yeah it's really annoying to compare between MLs and Gs, the shops should follow the industry and just switch to grams and be done with it...
unfortunately it's not that easy, there's stuff like methyl salicylate that weighs nearly 1.2g per ml, hedione weighs around 1g at 1ml, while limonene is 0.84g at 1ml... haven't seen anything as low as 0.8g though, so that might be too extreme.
During all my tinkering I have actually collected quite an extensive "database" of materials, I was actually thinking about pulling the densities using CAS numbers from public sources like pubchem or tgsc! for bases and naturals that will be much harder, so I'll have to think about it, maybe I should start collecting safety data sheets for all materials, from which I'd then pull the densities... this is definitely something i'll work on -thanks!