The smallest atom is helium at ~30pm
, a very large atom like caesium is ~225pm
. Salt obviously varies in size but let's say it's particularly fine at 100μm
then a helium atom is ~3 millionth of the size and a caesium atom is ~0.5 millionth of the size. So if a helium atom was as large as a grain of salt a grain of salt would be ~100m wide and for a caesium atom it would be ~16m wide.
I'm pretty sure my math is correct there