i agree with BigC, I don't like going by these "guidelines" as they should be different for every person, ever tank, every filter etc etc, but if i had to have a guideline then personally i would happily go up to 2" per gallon with small, relatively slim bodied fish, like tetras.
However, i personally think 12g is on the small side for danios, some may be small but they need alot of room to swim imho.
However, i personally think 12g is on the small side for danios, some may be small but they need alot of room to swim imho.