Key Transposition Calculator

Transpose key calculator: move chords, scales and guitar capo positions between any key by semitone, with note mapping and capo fret shown. Free, private.

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Every figure above is calculated locally in your browser from the assumptions shown. No inputs are sent anywhere. See the methodology section below for the formulas used.
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Direct answer

What does this calculator estimate?

Transposing a key means shifting every note by the same number of semitones: C to G is up 7 semitones, C to Eb is up 3, and Eb back to C is up 9. The shift wraps around the 12-note chromatic scale, so the answer is (target - original + 12) mod 12, and every note keeps its scale degree in the new key.

  • Transpose distance = (target key position - original key position + 12) mod 12 on the chromatic scale (Source: BoringToolsKit methodology)
  • C to G is up 7 semitones, and C to Eb is up 3 semitones (Source: BoringToolsKit methodology)
  • Shifting 12 semitones returns a key to the same pitch class, so all 12 transpositions of a key cover every major key exactly once (Source: BoringToolsKit methodology)
Chromatic semitone steps for common key transpositions
C to Eb shifts every note up 3 half-steps.
Transparent methodology

How this calculator works

Formula

semitones = (position(to) - position(from) + 12) mod 12. Example: position(C) = 0, position(G) = 7, so C to G is up 7 semitones; Eb to C is (0 - 3 + 12) mod 12 = 9.

Worked example

C to G: 7 semitones. C to Eb: 3 semitones. Eb to C: 9 semitones. C to C: 0, no change (same key). Every melody in C sounds the same, 7 semitones higher (a perfect fifth), in G.

Sources

Assumptions to verify

  • Keys are compared on the 12-note chromatic scale with enharmonic equivalents treated as one position
  • The result is the upward shift; transposing down is 12 minus the result

Frequently asked questions

How many semitones is C to G?

Seven. G is 7 chromatic steps above C, the interval called a perfect fifth.

Does transposing change the melody?

No. Every interval between notes is preserved; the whole melody shifts to a new register while staying musically identical.

Why transpose a song at all?

To fit a singer's range, match an instrument's key, or simplify the chords. The pitch moves; the musical structure does not.

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Related guide

Read the guide

Key Transposition: Semitone Shifts Explained

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Cite this tool

BoringToolsKit. “Key Transposition Calculator.” boringtoolskit.com/key-transposition-calculator/. Free to reference in articles, syllabi, and answer posts with a link.

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Worked example: C to Eb

The calculator stores the 12 key labels in a fixed chromatic order: C, C#, D, Eb, E, F, F#, G, Ab, A, Bb, B. Each label sits at a chromatic index: C is 0, D is 2, Eb is 3. To transpose from C to Eb, it finds index 0 for C and index 3 for Eb, then computes (3 - 0 + 12) mod 12 = 3. That gives 'up 3 semitones' and 'Equivalent to: 3 half-steps'. Musically that is the C minor third: every C, D, and E in your chart becomes Eb, F, and G.

The +12 in the formula handles the wrap-around case. Take F to C: F is index 5, C is index 0, so (0 - 5 + 12) mod 12 = 7, reported as up 7 semitones. Without the +12 the raw difference would be -5, and the modulo would still land on 7 in JavaScript for this case, but the explicit +12 keeps the result a positive step count in every input, including F# to F, which is (5 - 6 + 12) mod 12 = 11.

Limits worth knowing before you transpose

The label list uses fixed spellings, so enharmonic keys are not interchangeable the way theory would allow. There is no Db, D#, Gb, or A#; if your piece is in Db you pick Eb's slot (index 1 as C# or index 3 as Eb) and the step count still comes out right, but the printed key name will not match your sheet music's spelling. Similarly C# and Db both map to index 1.

The tool also reports only the shortest clockwise distance. B down to C is physically 1 semitone downward, but the calculator returns up 11 semitones, because it always measures forward in the chromatic cycle and only says 'no change (same key)' when the two keys match exactly. And it moves the key center only: transposing C to G shifts every note up 7 half-steps but keeps the mode, so a C major chart becomes G major, while a C minor chart becomes G minor. It will not convert major to minor or re-fingering for a capo.