‘Thus’ is used in presenting a logical argument in academic and sometimes in official writing. You can also use ‘therefore’ in much the same way. In all other contexts, written and spoken, ‘so’ is appropriate.

Thus is more formal and so can be used in a variety of situations. Hope this helps! :)

Both conjunctions imply that the clause coming after the conjunction logically follows from what came before, so in that way they are mostly interchangeable. But as Adrian says, "thus" is usually more formal than "so." Most native speakers of English would think it odd (but not incorrect) to use "thus" in casual conversation.

So can be used as a noun, conjunction (meaning 'in order that'), and as an adjective ( meaning true or accurate). When used as adverbs, so means to the extent that, whereas thus means in this way or manner.