Grams are ounces. Ounces are pounds. Milligrams are grams. Micrograms are milligrams. Picograms are micrograms.

the point of knowing the rough conversion is to be able to do head-math to get a close number. I use 30 a lot of the time, b/c most of the time a close estimate is all I need.

if you're cutting off the borders of your map, by all means, use a calculator

And important that Troy is used for metals (31.1) That counts when 1g of gold is nearly $120usd