No one is sure, since that wasn't mentioned by Plato.
But, we do know that when Plato said 'beyond the pillars of Hercules' he meant beyond what was known of the existing world; ie. on the edge of known land.
Given that, let's assume a person stands on the highest peak in the straits and looks westerly (it is assumed Plato meant that direction because he distinctly says "in front of" and in size it was 'greater than Asia and Libya [Africa] combined.') and on a clear day - that person could probably see for about 50 miles.
But, Plato also said that there were, I think about 10 kings/rulers of their individual (is)lands, that would mean at least 9 smaller islands and one big/main one. If they were all spread-out then we can "ballpark" an estimate of anywhere from 50 to perhaps 200 miles away.
It is also assumed that these islands (or Atlantis prime/Poseidon) were about in the middle of the Atlantic (hence the name Atlantis) so, it couldn't be any further than the "lands on the opposite continent" - the America's, which Plato also refer to.
This is all conjecture on my part, but, I think it is reasonable in its assumptions.
The Pillars of Hercules are the stones that mark the entrance to the Strait of Gibraltar. Plato was believed to have said that the Pillars of Hercules marked the entrance to the lost city of Atlantis.
sraits of gibraltar
The Greek philosopher Plato in his works Tinnaeus and Critias describes a land larger than Africa beyond the pillars of Hercules [Gibraltar straights] that its civilization was destroyed by a catastrophic flood 9000 years before his time after a war between the Greeks of Athens and the Atlantis, though some speculate whether the date was mistranslated and was supposed to be 900 years.
The Pillars of Hercules are situated in two different places. The Northern pillar is said to be the 'Rock of Gibraltar'. The location of the Southern pillar however, is disputed. The two most likely candidates are considered to be 'Monte Hacho' in Ceuta, and 'Jebel Musa' in Morocco.
Or rather the pillars of Hercules. The ancient name for two promontories at the eastern end of the Strait of Gibraltar and the entrance to the Mediterranean Sea. They are usually identified as Gibraltar in Europe and Jebel Musa in North Africa.
The Pillars of Hercules are the stones that mark the entrance to the Strait of Gibraltar. Plato was believed to have said that the Pillars of Hercules marked the entrance to the lost city of Atlantis.
Atlantis
Atlantis is a mythical island first mentioned by Plato. According to the story, Atlantis was located beyond the "Pillars of Hercules," which is now believed to refer to the Strait of Gibraltar. Therefore, it is not known or confirmed how far under sea level Atlantis might have been.
Atlantis is a legendary island that was said to have existed in the Atlantic Ocean, beyond the "Pillars of Hercules" (Straits of Gibraltar). However, there is no conclusive evidence to support the existence of Atlantis.
Ive heard Atlantis was named for being in the Atlantic ocean. And that it lies facing the Pillars Of Hercules.
There is no definitive location for the lost city of Atlantis as it is a legendary island that has never been proven to exist. According to Plato's writings, Atlantis was said to be located beyond the "Pillars of Hercules," which is now believed to be the Strait of Gibraltar in the Atlantic Ocean.
The Pillars of Hercules are now known as the Strait of Gibraltar.
YMB's house.
sraits of gibraltar
In Greek mythology, Hercules came to a mountain and instead of climbing the mountain, he used his club to smash through it. This created two mountains that were named the Pillars of Hercules.
sraits of gibraltar
The straights of Gibralta