Open C Tuning for Guitar

Open C runs C2, G2, C3, G3, C4, E4, in playing order. The lowest-pitched string is C2 (65.41 Hz) and the highest is E4 (329.63 Hz), measured against A4 = 440 Hz. Those are the exact target frequencies the tuner on this page listens for.

4 of the 6 strings move: E2 down 4 semitone(s) to C2; A2 down 2 semitone(s) to G2; D3 down 2 semitone(s) to C3; B3 up 1 semitone(s) to C4. Work through them in order, then go back and re-check the first string — retuning shifts the neck tension slightly, so the earlier strings drift as you go.

A wide-voiced C major with the root doubled across three octaves. The spread makes it unusually resonant for fingerstyle and it is a favourite for acoustic instrumental writing, though the big interval jumps make familiar shapes useless.

C2 is 65.41 Hz at concert pitch (A4 = 440 Hz). That's the fundamental — the string also produces harmonics above it, which is why a tuner reading the wrong octave usually means it locked onto a harmonic rather than the fundamental. This is the lowest string in this guitar tuning.

Spelling C, G, C, G, C, E, this stacks the root three times across three octaves and the fifth twice, leaving the third exposed on the single highest string. That distribution is what makes it unusually resonant — sympathetic vibration between the doubled roots and fifths is strong — and also what makes it fragile, since the chord's entire major quality hangs on one string. The interval jumps between courses are wide and irregular compared with standard, so no familiar shape survives and the tuning effectively has to be relearned. Fingerstyle composers accept that trade for the sustain and the unusually wide voicings it makes reachable in one hand position.