Speculative

What is William James Sidis's IQ?

William James Sidis is routinely credited with an IQ between 250 and 300 — sometimes higher. No test producing those numbers exists, and no scale extends that far. The figures were invented by journalists and have been recycled ever since.

250 – 300circulated range

Written and reviewed by the myfreeiqtest editors.

William James Sidis as a boy, a black and white head-and-shoulders portrait in a dark collared top.

William James SidisChild prodigy, mathematician

A quick, honest note. This number circulates online with no traceable origin. We publish it because you came to read it, and label it what it is: lore.

Where does the 250–300 number come from?

The documented facts need no exaggeration. Sidis entered Harvard at eleven, lectured the mathematics society on four-dimensional bodies the same year, and read widely in a large number of languages.

ClaimWhere it traces toHow solid

"IQ 250–300"Press speculation; no test recordWeak

Entered Harvard at elevenDocumented historical recordStrong

Table 1 · Every thread behind the figure, and how much weight it can carry.

The IQ figures attached to him are a different matter. They postdate his life, have no test behind them, and exceed the range any scale defines. A deviation IQ of 300 would describe a frequency of roughly one in a number far larger than the count of humans who have ever lived — it is not a rare score, it is an undefined one.

Sidis withdrew from academic life, worked clerical jobs, and wrote under pseudonyms until his death at forty-six. The press that had built him up spent years mocking the retreat. It is a bleak story, and the invented numbers are part of what made it one.

How rare would a 300 IQ be?

If the 300 end of that range were literally true, it would be extraordinarily rare — rarer than1 in ∞ people. That alone is a good reason to treat any confident-sounding celebrity IQ number with a raised eyebrow.

Figure 1 · The marker is dashed because the number is an estimate.

1 in ∞

Too rare to draw — a grid with one highlighted dot in ∞ would be a solid wall of gray.

Figure 2 · A 300 would make Sidis 1-in-∞ smart.

What a score like this would mean

A 300 would sit in the very superior · gifted range — about one person in ∞. Fill a large concert hall and you would expect nobody in the room to clear it.

See what that band actually means:What the top band means The full IQ scale

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