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The typical size of a hydrogen atom is a constant, and it is about a ten billionth of a meter.

Physics Facts, sourced to NIST.

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What it means

An atom has no hard edge, so its size is a statement about where the electron is likely to be found rather than a wall. The Bohr radius marks the distance at which the electron in a hydrogen atom spends much of its time. Line up ten billion of them and you have covered a meter, which is roughly the same ratio as a marble to the diameter of the Earth.

The claim comes from NIST.

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