Scale degrees · B♭ major
The ♭5 of B♭ is F♭
The ♭5 (flat five, written b5) of B♭ (B flat, Bb) is F♭ (F flat): a diminished fifth above the root.
B♭ — the root, 1F♭ — the ♭5
How to find it
Count letters first, the root included: B, C, D, E, F. A 5th lands on F.
Then the sound: a diminished fifth is 6 semitones above B♭, and the F that is 6 semitones up is F♭.
That is why it is F♭ and not E: E is the same key on the piano, but from B♭ it would be a 4th, not a 5th.
Where you meet it
The ♭5 halves the octave: a tritone above B♭. It is the 5th of the half-diminished and the diminished chord.
In B♭m7♭5:
B♭ · D♭ · F♭ · A♭
The ♭5 in every key
| Key | The ♭5 |
|---|---|
| C | G♭ |
| G | D♭ |
| D | A♭ |
| A | E♭ |
| E | B♭ |
| B | F |
| F♯ | C |
| D♭ | A𝄫 |
| A♭ | E𝄫 |
| E♭ | B𝄫 |
| B♭ | F♭ |
| F | C♭ |
Every degree of B♭
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