The world's smallest island

Bishop Rock

To answer this question we must first answer 'What is an island?'

A hunk of rock classifies an an island if one of two conditions are true:

1. It is inhabited.
2. It has to equal the size of the summer's pasturage of at least one sheep which is equal to two acres according to an 1861 bureaucratic classification.

Now that that is out of the way, the world's smallest island is Bishop Rock  located of the south west point of the United Kingdom.

Bishop Rock houses a manned lighthouse on a 46 x 16 meter expanse of rocks that combined makes up the world's smallest island.