B♭ (musical note)

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For other uses, see B-flat.

B♭ (bee-flat; also called si bémol) is the eleventh semitone of the Western chromatic scale.

It lies a diatonic semitone above A and a chromatic semitone below B, thus being enharmonic to A♯ although in some musical tunings, B♭ will have a different sounding pitch than A♯.

When calculated in equal temperament with a reference of A above middle C as 440 Hz, the frequency of the B♭ semitone is approximately 466.164 Hz. See pitch (music) for a discussion of historical variations in frequency.

While orchestras tune to an A provided by the oboist, wind ensembles usually tune to a B-flat provided by a low brass instrument, typically a tuba.

In much of continental Europe (especially Germany), this pitch is designated B, with H used to designate the Anglo-American B-natural. See B (musical note) for an explanation.