Key Transposer / Capo Calculator
Transpose chord names up or down by semitones (capo positions).
Overview
The key transposer takes a chord chart and shifts every chord up or down by a chosen number of semitones. Paste in "C G Am F" and ask for +5 semitones, and you get "F C Dm Bb". Ask for -2 semitones from "G D Em C" and you get "F C Dm Bb" again. It's the simplest possible operation in functional harmony, but doing it manually on a full song with extensions and slash chords is tedious.
It doubles as a capo calculator for guitarists: if you transpose down 4 semitones and put the capo on fret 4, you sound in the original key while fingering the new (easier) shapes. Singer-songwriters use the tool to find a key that suits a vocalist's range; cover bands use it to match a track's original recording to an instrument's strong keys.
How it works
Western music has 12 semitones to the octave. Transposing by n semitones moves every note up or down by n positions on the chromatic scale. The transposer parses each chord into its root note, quality (major, minor, diminished, etc.), and extensions or slash bass, then rotates only the root and slash bass by n semitones. Quality and extensions are preserved exactly.
Enharmonic spelling becomes a choice: transposing C up two semitones produces D (one sharp parent key) rather than something exotic. The tool picks spellings that match the target key's conventional sharps or flats, so the output reads cleanly. Capo positions are derived directly from the semitone shift: capo on fret n raises every open chord by n semitones, so transposing down n and capoing up n is sonically a wash.
Examples
C G Am F +5 semitones → F C Dm Bb
G D Em C -2 semitones → F C Dm Bb
Cmaj7 F#m7b5 G7 Am +3 semitones → Ebmaj7 Am7b5 Bb7 Cm
D/F# Bm A G -2 semitones → C/E Am G F
FAQ
Should I transpose up or down for a male/female vocal?
It depends on the singer, not the gender. Test the highest and lowest notes of the melody against the singer's comfortable range; transpose until both sit comfortably.
Why does the same chord get different spellings sometimes?
A# and Bb sound identical but read differently. The tool chooses the spelling that fits the new key's sharps or flats, so a song originally in F (which uses Bb) stays in flats after a small transposition.
How do capo positions relate to transposition?
Capo on fret n shifts every open chord up n semitones. To play a song in C while using G chord shapes, capo at fret 5 — that's C as G transposed up 5 semitones.
Does this work for chord charts with slash bass?
Yes. Both the chord root and the bass note are shifted by the same interval, preserving the voicing relationship.
What about Nashville Number notation?
Numbers are already key-independent, so transposing means just choosing a new key — no math needed on the chart itself.