What does transposing a key mean?

Transposing shifts every note and chord in a piece by the same interval — a fixed number of semitones up or down — so the music sounds the same relative to itself but at a different overall pitch. A song in C major transposed up 7 semitones becomes G major; the I–IV–V–vi chord progression (C–F–G–Am) becomes G–C–D–Em.

How is the transposition interval calculated?

The calculator finds the pitch-class index of both keys (C=0, C#/Db=1 … B=11) and computes (targetPc − sourcePc + 12) mod 12. That gives the number of semitones to add to every chord root. The same offset is applied to every degree of the diatonic scale, preserving each chord quality (major, minor, diminished).

Why does the same note have two names — like C# and Db?

C# and Db are enharmonic equivalents: they represent the same piano key but are spelled differently depending on context. Keys with sharps in their key signature (G, D, A, E, B) conventionally use sharp spellings; keys with flats (F, Bb, Eb, Ab, Db, Gb) use flat spellings. The calculator follows these conventions automatically, and you can override the preference in the Chord Chart tab.

Can I transpose by a full octave?

Yes — entering +12 or −12 semitones moves every chord up or down by one octave. The note names stay identical, only the register changes. This is useful when a song sits too high or too low for a singer and you want to move it by an exact octave without changing the key.

How do I use this as a guitar capo calculator?

A capo on fret N raises every open chord by N semitones. If the original key is G and you want to play open C-shape chords with a capo, transpose from C to G (+7 semitones) to find which chord shapes to use — then place the capo on fret 7. Alternatively, transpose from the original key to C (or whichever open-chord key suits your playing) and use that capo fret.

What modes are included in the Scale Builder?

The Scale Builder covers all seven diatonic modes (Ionian/Major, Dorian, Phrygian, Lydian, Mixolydian, Aeolian/Natural Minor, Locrian), Harmonic Minor, Pentatonic Major, Pentatonic Minor, Blues, Whole Tone, and the Diminished (half-whole) scale — 13 scales in total. For each scale it shows the semitone offsets, interval names, and (for 7-note scales) the full set of diatonic triads.

What is the Key Transpose Calculator?

Free key transpose calculator: shift a song from one key to another, transpose a chord chart by any number of semitones, and view the complete diatonic scale and triads for any key or mode. Runs entirely in your browser. It runs free in your browser on Gera Tools, with nothing uploaded.

Key Transpose Calculator

Name: Key Transpose Calculator
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

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Transposing music to a different key is one of the most fundamental tasks in music theory — whether you are arranging a song for a singer with a different vocal range, switching to guitar-friendly open chords with a capo, or writing a lead sheet that works for a Bb trumpet. This calculator handles the whole process in three interconnected tools: a Key Transposer that maps every diatonic chord from one key to another, a Chord Chart Transposer that shifts an entire sheet of chords by any semitone interval, and a Scale Builder that shows the notes and triads for any of 13 scales or modes.

How transposition works

Every musical key is built on a pitch class — one of the 12 equally-spaced semitones in an octave (C, C#/Db, D, D#/Eb, E, F, F#/Gb, G, G#/Ab, A, A#/Bb, B). To transpose from key A to key B, the calculator computes:

semitones = (targetPitchClass − sourcePitchClass + 12) mod 12

That single offset is then added to every chord root and scale degree in the original key. Because chord quality (major, minor, diminished) depends on the interval structure of the scale rather than the absolute pitch, every chord keeps its function: the I chord stays the I chord, the IV stays the IV, and so on — just at a new pitch level.

Chord chart transposition in detail

The Chord Chart tab recognises standard chord symbols: bare roots like C or F#, minor chords (Am, Dbm, Bmin), dominant 7ths (G7), major 7ths (Cmaj7), minor 7ths (Am7), diminished (Bdim, Fdim7), augmented (Caug), and suspended chords (Dsus2, Asus4). Everything else — lyrics, bar lines, annotation text — is passed through untouched, so you can paste a real lead-sheet and get a clean transposed version in seconds.

Worked example

A song in E major uses the chords E – B – C#m – A (the classic I–V–VI–IV pop progression). A vocalist needs it in G major.

E to G is +3 semitones (E=4, G=7, 7−4=3).
E (I) → G
B (V) → D
C#m (VI) → Em
A (IV) → C

Result: G – D – Em – C — the same emotional relationship between chords, now in a singable key.

Scale and mode reference

Each scale is defined by its interval pattern — the sequence of semitone steps between consecutive scale degrees. Major (Ionian) uses 2-2-1-2-2-2-1 (whole-whole-half…). Dorian replaces the major sixth with a minor sixth and the major seventh with a minor seventh, giving it its characteristic jazz and Celtic sound. The Blues scale adds a flattened 5th (the “blue note”) to the minor pentatonic. The calculator displays all offsets from the root and derives the diatonic triads automatically by stacking every other scale degree.

Formula note

Frequencies of individual notes within a key follow the equal-temperament formula f = 440 · 2^((n−69)/12), where n is the MIDI note number (A4 = 69). Transposing by k semitones multiplies the frequency by 2^(k/12) — up 7 semitones (a perfect fifth) scales frequency by approximately 1.498, which is why a perfect fifth sounds so harmonically stable: it closely matches the 3:2 pure ratio from just intonation.