This is the real, secret, reason your math teacher told your class to stay awake.
It wasnt so you could share 8 apples with 9 people (who does that) they were trying to help you do drugs.
I was lucky, my teachers were hippies and told us math would help with drugs. Thats why in highschool I aced everything straight through pre-calc
In a base 10 number system with positional multipliers, like the one we have, you just move the decimal to adjust by powers of ten. Theres a thousand milligrams in a gram so just move the dot 3 spaces, 1.000 grams = 1000 mg