How this calculator works
Transposition adds the same number of semitones to every note, so the melody keeps its shape and moves to a new key. A key change is the same operation measured between the two tonics: from C up to G is seven semitones, while from C down to G is five. Both reach G, and the choice of direction usually depends on the range of the singer or the instrument. This page names the new notes with the spelling you choose, so the result can be read directly in the new key.
Formula
new note = (old pitch class + semitones) mod 12. For a key change, semitones = (new tonic - old tonic) mod 12 moving up, or that value minus 12 moving down. Pitch classes number the notes chromatically from C = 0 to B = 11.
Worked example
Transposing C, D, E and F up two semitones gives D, E, F# and G. Transposing G, A and B up five semitones gives C, D and E. Changing key from C to G with the up direction moves seven semitones, so C, E and G become G, B and D, which is the same chord transposed a fifth.
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Frequently asked questions
Why is the semitone count sometimes negative?
A downward transpose is shown as a negative number because the notes move down. The resulting note names are the same as going up by the complement, but the octave and the direction of the melody differ. A singer transposing a song down a tone needs the melody a whole step lower, not a whole step higher.
What is the difference between transposing notes and transposing a chord?
The arithmetic is identical; the difference is that a chord also carries a quality, such as major or minor, that has to stay attached to its root. The chord transposer page handles that. This page moves any list of notes, which is what you need for melodies and bass lines.
Should I use sharps or flats?
Use the spelling that matches the new key. Keys on the sharp side, such as G, D and A, want sharps; keys on the flat side, such as F, Bb and Eb, want flats. The spelling field changes only the names, not the pitches.
How do I transpose by an octave?
Add or subtract twelve semitones. The note names repeat and the octave number changes, which this page does not show because it works on pitch classes. For a full octave shift, use the semitone or note frequency page to track the octave number as well.