Guitar tuning

Open C Tuning (C-G-C-G-C-E)

Open C tunes the strings to C-G-C-G-C-E, a C major chord spread across a very wide range. What sets it apart from the other open tunings is the sixth string: it drops two whole steps, from E to C. That is the largest drop in the guitar catalogue on this site, matched only by the Celtic C-G-D-G-A-D tuning. Both its sound and its one practical problem come from that.

🎸 Open the tuner in this tuning

The tuner opens already preconfigured; you only need to allow microphone access.

Strings and frequencies

String Note Hz
String 1 E4 329.63 Hz
String 2 C4 261.63 Hz
String 3 G3 196.00 Hz
String 4 C3 130.81 Hz
String 5 G2 98.00 Hz
String 6 C2 65.41 Hz

The sixth drops two whole steps: what that does to the tension

The sixth string goes from E (82.41 Hz) to C (65.41 Hz). That is four semitones, two whole steps: the only other tuning on this site that moves a single string that far is the Celtic C-G-D-G-A-D, which does exactly the same.

String tension is proportional to the square of the frequency, so that drop takes 37 % of the tension off it. On a normal set the sixth string ends up slack: it wobbles under hard picking, buzzes against the first few frets, and goes sharp the moment you press it down firmly.

That is the real problem with Open C, and it is not the one people usually worry about. The guitar is in no danger at all — three strings come down and only one goes up a half step, so the total load is well below standard tuning. What suffers is the sound of the bass string.

What gauge keeps the sixth string from going slack

The arithmetic is doable. To get back at C the tension the string had at E, its mass per metre has to be multiplied by 1.59, and since mass grows roughly with the square of the diameter, that means multiplying the gauge by 1.26.

Applied to a 0.053 sixth, the one in a light acoustic set, that gives 0.067. That would be the gauge that restores the tension exactly.

In practice almost nobody goes that far, and there is a reason: a 0.067 usually will not sit in a nut slot cut for a 0.053, so the slot would have to be opened and the setup checked. The realistic advice comes in steps.

One caveat on the arithmetic: the mass of a wound string grows with the square of the diameter only approximately, since it also depends on the core-to-wrap proportion and the material. The 0.067 is a good orientation, not an exact manufacturer figure.

The other two strings that come down — the fifth and the fourth, a whole step each — lose 21 % of their tension, which is what happens in any tuning dropped a whole step and is easily handled by normal gauges.

What is Open C tuning used for?

For three specific things, and they are worth knowing before you restring.

The first is range. Open C reaches a C two whole steps below standard E without changing guitars, and keeps the same high E on top. That widening at the bottom is what gives it the almost piano-like sound that modern acoustic fingerstyle and much of post-rock choose it for.

The second is drone accompaniment. With three open strings on C and two on G, you can move up the neck letting them ring and almost everything fits. It is the same idea as the Celtic tunings, but over a defined major chord instead of a modal sound.

The third is one-finger chords. Since all six open strings already form a C major, a straight barre at any fret gives a complete major chord: fret 2 gives D, fret 4 gives E, fret 5 gives F, fret 7 gives G. That makes it comfortable for slide and for anyone accompanying their own singing.

What it is not good for is transferring what you already know. Four of the six strings change note, so standard chord shapes do not work. If you want a small change, Drop D or Double Drop D are far closer to home.

What chord do the open strings make?

C, G, C, G, C and E: a C major chord with three Cs, two Gs and a single E.

That distribution has a practical consequence almost nobody mentions. The third of the chord — the E, the only thing making it major — lives on one string, the first. Everything else is root and fifth.

So if you damp or skip the first string, what is left is neither major nor minor but a bare C of root and fifth, which fits a melody in C minor as comfortably as one in C major. And if you take that first string down one more semitone, from E to E flat, the whole tuning becomes C minor.

Against Open D, which distributes its third in a similar way, Open C sits two whole steps lower at the bottom and so sounds considerably bigger. Against the Celtic C-G-D-G-A-D tuning, which starts from the same low C, the difference is that here there is a third and the chord has made up its mind.

What songs use Open C tuning?

This needs care, because most of the lists in circulation mix Open C up with a variant of it.

The songs most often cited as Open C — Led Zeppelin's Friends and Bron-Yr-Aur — are in fact in C-A-C-G-C-E, which is not quite this tuning: the fifth string stays on A instead of dropping to G. That A turns the open chord into a C6 and gives it a distinctly different, more suspended colour.

It is a very close variant and worth knowing about, but if you tune following this page and then put one of those songs on, something will not line up. The difference is one string.

For Open C proper, with the fifth on G, we have no recordings we can confirm against a solid source, and we would rather not pad the list with second-hand attributions. It is heavily used in contemporary instrumental fingerstyle, where the repertoire travels in arrangements rather than in well-known songs.

How to tune to Open C from standard

Four strings move: three go down and one goes up a half step.

Start with the second, the only one that rises: a half step, B to C. That is one fret.

Drop the fourth a whole step, D to C: it should match the second string you have just tuned, one octave below.

Drop the fifth a whole step, A to G: it should match the open third string, one octave below.

Finish with the sixth, which moves furthest — two whole steps, E to C. It should match the fourth string, one octave below. Go slowly: a string that slack takes a while to settle and drifts while you tune the others, so you will need two or three passes over it.

The third and first strings are untouched: they stay on G and E.

Open C on ukulele

The ukulele has an Open C too, and the contrast is telling. On ukulele it is G-C-E-G, the same C major chord, and you get there by moving a single string if the ukulele is already in Low G, or two coming from the reentrant standard.

In other words, what on guitar demands the biggest string drop in the catalogue — matched only by the Celtic C-G-D-G-A-D — is on ukulele one of the smallest changes there is. If what you want is to hear how playing over an open C major feels before restringing the guitar, the ukulele is the shortcut.

The ukulele Open C page has each string frequency and the tuner preconfigured, exactly like this one.

How it sounds

It sounds big, resonant and full-bodied thanks to that low C and the repeated octaves. It is a favourite of modern acoustic fingerstyle and of anyone after an almost piano-like guitar sound.

The price of that width is that the guitar loses firmness at the bottom. Properly strung it sounds spectacular; on any old set it sounds hollow. Along with the Celtic C-G-D-G-A-D, it is the tuning on this site where string gauge matters most.

Styles and genres

Acoustic fingerstyle Folk Post-rock Singer-songwriter Slide

Recommended string gauges

The string that decides everything is the sixth, which loses 37 % of its tension dropping to C. A 0.013-0.056 set is the sensible minimum, and a single 0.060 to 0.062 sixth over an otherwise normal set is the compromise that works best.

The fifth and fourth come down a whole step each and lose 21 %: normal gauges handle that with nothing special required.

The second is the only string that goes up, by a half step, gaining around 12 % of tension. That is a small change and needs nothing.

Tuning tip

Watch the sixth string in particular: being so low, it is the most prone to buzzing and drifting. If it rattles, go up a gauge on that string alone rather than the whole set, and check the action at the first fret before calling the tuning done.

Frequently asked questions

What is Open C tuning used for?

Three things: gaining low range without changing guitars — it reaches a C two whole steps below standard E — accompanying with open strings ringing over a C major chord, and getting major chords from a one-finger barre at any fret. It is the favourite of modern acoustic fingerstyle and post-rock for its almost piano-like sound.

What songs use Open C tuning?

Carefully: the ones cited most often — Led Zeppelin's Friends and Bron-Yr-Aur — are actually in C-A-C-G-C-E, a variant where the fifth string stays on A instead of dropping to G, and they sound different. For Open C proper we have no recordings we can confirm against a solid source; it is mainly an instrumental fingerstyle tuning, where the repertoire travels in arrangements rather than in well-known songs.

What string gauge do you need for Open C?

The sixth loses 37 % of its tension dropping two whole steps to C, so a normal set leaves it slack. A 0.013-0.056 is the minimum; a single 0.060 to 0.062 sixth is the compromise that works best. Restoring the tension exactly would take around a 0.067, which usually will not fit the nut slot.

Is Open C tuning bad for your guitar?

No. Three strings come down and only one goes up a half step, so the total load on the neck and the top is well below standard tuning. The problem with Open C is not safety but sound: the sixth string goes slack and has to be compensated for with gauge.

How do you tune a guitar to Open C?

Four strings move. The second goes up a half step from B to C; the fourth comes down a whole step from D to C; the fifth comes down a whole step from A to G; and the sixth comes down two whole steps from E to C. The third and first stay on G and E. Go over the sixth two or three times, since it takes a while to settle.

What chord do the open strings make in Open C?

C, G, C, G, C and E: a C major with three Cs, two Gs and a single E. The third of the chord sits on one string only, the first, so damping it leaves a C that is undecided between major and minor — and taking that string down a semitone to E flat turns the whole tuning into C minor.

Is guitar Open C the same as ukulele Open C?

It is the same C major chord laid out differently: on ukulele it is G-C-E-G. The practical difference is enormous — on guitar Open C carries the biggest string drop in the catalogue — tied with the Celtic C-G-D-G-A-D — and on ukulele it takes moving one string, or two coming from the reentrant standard.

Is Open C good for slide guitar?

Yes. Since all six open strings form a complete C major, a straight barre with the slide at any fret gives a major chord with no tilting of the bar. What needs care is the sixth string: if it is slack it wobbles under the weight of the slide, so gauge matters more here than in Open D or Open E.

Related tunings

Sources

  1. The tension changes and the equivalent gauge on this page are calculated from the frequencies in the table above, which are the ones the tuner itself uses. String tension is proportional to the square of the frequency, and the mass per metre of a wound string grows roughly with the square of its diameter.

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