Sharps or flats? Choosing # and b in chord charts

On a piano, C# and Db are the same black key. In a chord chart, though, one spelling usually reads better than the other. Here is how to choose.

Same sound, two names

There are 12 different notes in an octave but only 7 letters (A to G). The five notes between the letters get two names each: C#/Db, D#/Eb, F#/Gb, G#/Ab, and A#/Bb. Two names for the same pitch are called enharmonic equivalents.

A guitar or keyboard plays them the same way, so neither spelling is "wrong". But the right one makes a chart quicker to read and shows how the chords relate to each other.

In plain text, # stands for sharp (♯) and a lowercase b for flat (♭). Chord Transposer reads both forms and writes # and b.

The basic rule: follow the key

A major scale uses each letter exactly once. In the key of F, the notes are F, G, A, Bb, C, D, E. Writing A# instead would use the letter A twice and skip B, so the fourth chord of F is Bb, not A#.

F    Bb   C7   F

Key of F: reads naturally

F    A#   C7   F

Same sound, but harder to read

So: in a sharp key, write black-key chords with #. In a flat key, write them with b.

Sharp keys and flat keys

Each key (and its relative minor) uses either sharps or flats, never both:

# or b in the key	Sharp keys (major / minor)	Flat keys (major / minor)
0	C / Am
1	G / Em	F / Dm
2	D / Bm	Bb / Gm
3	A / F#m	Eb / Cm
4	E / C#m	Ab / Fm
5	B / G#m	Db / Bbm
6	F# / D#m	Gb / Ebm
7	C# / A#m	Cb / Abm

The keys with 6 and 7 accidentals have twins: F# = Gb, C# = Db, and Cb = B. Most charts use F# (or Gb), Db, and B.

A quick memory aid: F and every key whose name contains b are flat keys. The other keys, apart from C, are sharp keys.

Chords outside the key

Songs often borrow chords from outside the key. Common habits:

Borrowed chords from the minor key are written with flats. In C, the chords from C minor are Bb, Ab, Eb, and Fm — not A#, G#, or D#.
Rising lines are usually written with sharps: C C#dim Dm.
Falling lines are usually written with flats: D Db C, or a bass line like C C/B C/Bb F/A.

When in doubt, pick the spelling that keeps the letters moving in a step-by-step order.

The #/♭ setting in Chord Transposer

The app has three choices for how transposed chords are spelled:

Setting	`F Bb C7 Dm` +3 becomes	Rule
Original	G# Db D#7 Fm	Follows the source: a chord written with b stays with b (Bb → Db). A chord with no # or b gets # (F → G#).
Prefer #	G# C# D#7 Fm	Always #.
Prefer b	Ab Db Eb7 Fm	Always b.

The example moves a chart from F to Ab, a flat key, so Prefer b gives the expected spelling.

How to choose: look up the new key in the table of sharp and flat keys. If it is a flat key, choose Prefer b; if it is a sharp key, choose Prefer #. Then check the chords outside the key and fix any by hand.

When Transpose is 0, Prefer # and Prefer b only rewrite chords that already have # or b. Use this to clean up a chart that mixes the two, for example Db → C#.

See also: chords in every key, which spells every chord from its key.