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The following table gives the theoretical frequency for each note on the piano starting with the lowest note. Each octave is double the frequency of its first note, e.g. A4 has a frequency of 440 which is twice the frequency of A3 at 22. Each octave has 12 semitones between giving a ratio of the 12th root of 2 between adjacent notes. In practice, actual frequencies differ from the theoretical ones due to inharmonicity, octave stretch, false beats or piano age.
Although A4 is listed here with a frequency of 440 Hz, the Historical A page gives other values of this note throughout history.