Key Transposition Calculator
Transposing moves a note or key up or down by a fixed interval. This calculator takes a starting note as a chromatic number from 0 (C) to 11 (B) and a semitone shift (positive to move up, negative to move down), then returns the transposed note, the octave shift, and the interval name for the move. It is exact, twelve-tone equal-temperament arithmetic, so it works for melody transposition, fitting a vocal range, or converting between written and sounding pitches on a transposing instrument.
Transposition logic
transposed index = (note + shift) mod 12 (wrapped positive)
octave shift = floor((note + shift) / 12)
interval = interval name for (shift mod 12, ignoring sign)
note name = chromatic name of transposed index
Adding the shift and wrapping within 12 gives the transposed pitch class. The octave shift tracks whole octaves moved. Interval names map a within-octave semitone distance to its musical name.
Transposition context
- 1 semitone is a minor second; 2 is a major second.
- 7 semitones is a perfect fifth; 5 is a perfect fourth.
- 12 semitones is a full octave, returning to the same note name.
- A B-flat instrument transposes by 2 semitones to concert pitch.
- Transposing changes the key signature; the pitch relationships stay fixed.
Transposition: frequently asked questions
What does transposing a key mean?
Transposing shifts every note in a piece up or down by the same interval, moving it to a new key while keeping the melody and harmony intact relative to each other. Singers transpose to fit their range; instrumentalists transpose for transposing instruments. This calculator moves a note by the number of semitones you choose.
How do I transpose by semitones?
Add the semitone shift to the starting note's chromatic number (0 for C through 11 for B), then wrap within 12. A positive shift moves up; a negative shift moves down. For example, C (0) shifted up 2 semitones becomes D (2). The calculator does the wrapping and names the result.
What interval does a semitone count correspond to?
Common intervals are: 1 semitone is a minor second, 2 is a major second, 3 a minor third, 4 a major third, 5 a perfect fourth, 7 a perfect fifth, and 12 a full octave. The calculator reports the interval name for shifts within an octave so you know the musical distance.
Why might I transpose for an instrument?
Transposing instruments such as the B-flat trumpet or clarinet sound a different pitch than written. To make a part sound in concert pitch you transpose by a fixed interval. For a B-flat instrument that is 2 semitones; enter that shift here to convert between written and sounding notes.
Does transposition change the key signature?
Yes. Moving to a new key usually changes the number of sharps or flats. After transposing the tonic with this tool, use the key signature calculator to find the new key signature. The pitch relationships within the music stay the same.
Official sources
- Library of Congress: Music Theory Reference Collections.
- U.S. National Park Service (music education resources): Music Preservation.
Reviewed by the CalculatorHub team, edited by James Graham, 16 June 2026. See our methodology.