how long does something have to be to be considered a dissertation
A dissertation is a subject you chose for yourself. The first usage of the word in the English language in 1651 also gives a useful starting definition: “an extended written treatment of a subject”.
There are some obvious differences: an essay is relatively short – usually 1500 to 2500 words – and you are told clearly what to do by someone else. For example: Describe and evaluate major theories of globalisation.