How does a guitar capo work?

A capo clamps across all six strings at a chosen fret, effectively raising the nut. Every open string — and every chord shape played above the capo — sounds higher by one semitone per fret. Placing the capo on fret 2, for example, raises all pitches by a whole tone (two semitones), so a C-shape chord sounds like a D.

What is the transpose formula used here?

Two mirror formulas cover both directions. To find what open shape to play: open_root = (sounding_root - capo_fret) mod 12. To find what a shape sounds like: sounding_root = (open_root + capo_fret) mod 12. Both use modular arithmetic on the chromatic scale (12 notes per octave), which is why the result "wraps around" from B back to C.

How is the root frequency calculated?

The tool uses the standard equal-temperament formula f = 440 x 2^((n - 69) / 12), where n is the MIDI note number and A4 = 69. Middle C (C4) is MIDI 60, so a D4 root (two semitones above C4) gives n = 62 and f = 440 x 2^((62-69)/12) = approximately 293.66 Hz.

Does the capo change the chord quality (major, minor)?

No. A capo transposes pitch only — it shifts every note up by the same number of semitones, preserving all intervals within the chord. A minor shape played above the capo still sounds as a minor chord; only the root note name changes.

Which capo fret gives the easiest shapes?

Capo frets 1 through 5 are most common because they keep the chord shapes in the open-position zone (C, D, E, G, A, Am, Em, etc.). The "all capo options" table in the calculator highlights the open-shape hint for each fret so you can spot at a glance which position lets you use a familiar fingering.

Can this calculator handle flat keys?

Yes. Toggle "Show flat spellings" and every note is displayed in flat notation (Bb, Eb, Ab, Db, Gb) instead of sharps. The underlying chromatic arithmetic is identical — only the display label changes.

Capo Transpose Calculator

A capo transpose calculator solves the everyday guitarist’s problem: “I know a song is in E-flat, but I find barre chords awkward — can I use a capo and play open shapes instead?” This tool gives you the precise fret and the exact chord shape to finger, with the sounding root frequency shown in Hz so you can double-check against a tuner or DAW.

How it works

A capo acts as a moveable nut. Clamping it on fret N raises every open string by N semitones — one fret equals one semitone in equal temperament. The 12-note chromatic scale wraps around mod 12, which gives two clean formulas:

To find the open shape when you know the target chord:

open_root = (sounding_root − capo_fret) mod 12

To find the sounding chord when you know the open shape and capo:

sounding_root = (open_root + capo_fret) mod 12

Root frequency uses the equal-temperament formula derived from A440:

f = 440 × 2^((n − 69) / 12)

where n is the MIDI note number (A4 = 69, C4 = 60). The same formula that governs piano tuning, DAW pitch correction, and electronic tuners is what the calculator uses here — so the Hz readout is the internationally accepted reference pitch.

Worked example

Suppose a singer needs the song in B-flat major (Bb) but you want to avoid the barre chord. Using the calculator:

Set target sounding note to Bb, quality to major.
Try capo fret 3 → open shape = G major (a very easy open chord).
Result: play a G-shape with the capo on fret 3, and the guitar sounds a Bb.

Frequency check: Bb4 = MIDI 70, so f = 440 × 2^((70 − 69) / 12) = 440 × 2^(1/12) ≈ 466.16 Hz.

Target chord	Capo fret	Open shape to play
D major	2	C major
E major	4	C major
F major	1	E major
G major	5	D major
Bb major	3	G major
Eb major	6	A major

The “all capo options” table inside the calculator shows every fret from 1 to 7 at once, making it easy to pick the open shape that suits your playing style.

Formula note

The modular arithmetic works because the 12-note chromatic scale is a cyclic group of order 12. Adding or subtracting semitones always wraps at 12: note index 11 (B) plus 2 semitones = index 1 (C#), not 13. The JavaScript expression ((idx % 12) + 12) % 12 handles negative values correctly — for example, C (0) minus 3 semitones wraps to A (9) rather than −3.

The note-frequency formula is the standard equal-temperament definition used by the International Organization for Standardization (ISO 16) and every modern tuning reference since the adoption of A440 in 1939.