Chord Transposer (change the key of a chord chart)

Understanding the chord transposer — concept and principle

This tool moves a whole chord chart up or down by a number of semitones while keeping every chord type. It is used to put a song into a singer's range, to switch to a key with easier guitar shapes, or to work out which capo fret lets you keep the original shapes.

How it is calculated

1. Each chord is split into a root (A–G with an optional ♯ or ♭), the rest of the symbol (m7, maj7, sus4 …) and an optional slash bass.
2. The root and the bass are turned into pitch classes 0–11, shifted by the number of semitones, and wrapped round with modulo 12.
3. The rest of the symbol is kept exactly as typed.
4. Spelling: in automatic mode, the new key of the first chord decides. Keys F, B♭, E♭, A♭ and D♭ major (and D, G, C, F, B♭, E♭ minor) use flats; others use sharps. You can force sharps or flats.
5. Capo fret = semitones modulo 12, so a move down gives a high fret number.

The principle

Transposing adds the same interval to every note, so all the distances between notes stay the same. That is why the chord types and the sound of the progression do not change, only the pitch. Working in pitch classes makes the arithmetic simple: twelve semitones bring you back to the same note name, so +2 and −10 give the same names an octave apart. A capo works the same way on a guitar: clamping fret N raises every string by N semitones, so the old shapes sound N semitones higher.

Worked example

Default inputs: C G/B Am7 Fmaj7 Dm7 G7sus4, move +2 semitones, automatic spelling.

1. The first chord C (0) + 2 = 2 = D. D major uses sharps, so sharps are used.
2. G/B: G (7) + 2 = 9 = A; B (11) + 2 = 13 → 1 = C♯, giving A/C#.
3. Am7 → Bm7; Fmaj7 (5 + 2 = 7) → Gmaj7; Dm7 → Em7; G7sus4 → A7sus4.
4. Result: D A/C# Bm7 Gmaj7 Em7 A7sus4; first chord key D; capo 2; 6 chords changed.

How to read the result

The new chart sounds the same song two semitones higher. If you would rather keep playing the old shapes, put a capo on the shown fret. Check the first and last chords: they usually tell you the key. If the first chord is not the key centre, the automatic spelling may pick the wrong set of accidentals, and you can force sharps or flats instead.

Common mistakes

• Counting a whole tone as 1 instead of 2 semitones.
• Forgetting to move the bass note of slash chords.
• Expecting a capo to lower the pitch; it can only raise it.
• Typing chords with letters stuck to words or lyrics, which are then skipped.

Frequently asked questions

Should I transpose up or down?

Either works. Up 2 and down 10 give the same note names. Pick the direction that suits the singer's range.

What does the capo number mean?

Play the original shapes with a capo on that fret and the guitar sounds in the new key.

Why do some results use flats and others sharps?

The spelling follows the new key's signature, so B♭ major uses flats and D major uses sharps.

Sources: S. Kostka, D. Payne & B. Almén, Tonal Harmony, 8th ed. (McGraw-Hill, 2018), ch. 1 (intervals, key signatures, circle of fifths)