Open C is one of the less commonly used open tunings. However, it is an interesting tuning as it expands the tonal range on the guitar more than the most common tunings of standard tuning, Open G, and Open D. It is often used in blues and folk music and like all the open tunings it is well suited to fingerstyle guitar and playing with a slide. How to tune to Open C Open C tuning tunes the strings of the guitar so that when all the strings are played open it forms a C Major chord. The C Major chord is formed from the three notes which make up the C Major triad, these are the 1st, 3rd and 5th notes of the C Major scale, which are C, E and G respectively. Thus, each of the guitar strings in open D tuning will be tuned to one of these three notes.