Open C tuning is, from the low (6th) string to the high (1st) string, C G C G C E.
How do I tune my guitar to Open C?
Start in standard tuning. Lower the 6th string (E) to C, the 5th string (A) to G, the 4th string (D) to C, and raise the 2nd string (B) to C. Strum open for a big, deep C major chord — huge and orchestral (John Butler, Devin Townsend).
What is Open C tuning good for?
A deep, ringing open C major — massive, orchestral acoustic and ambient tones.