Before FIDE will give the Grandmaster title to a player, the player must have an Elo chess rating of at least 2500 at one time and three favorable results (called norms) in tournaments involving other Grandmasters, including some from countries other than the applicant's.
However, in general, it is believed and research indicates that top grandmasters usually have very high IQs. A person with average IQ is expected to reach a maximum rating of about 2000 in chess. Strong grandmasters with a rating of around and over 2600 are expected to have an IQ of 160 plus.