Open G, from the short 5th string to the 1st, is g D G B D. Strum the open strings and you get a G chord, which is the whole point. The little 5th string is a high G that starts at the 5th fret and mostly just rings along.
| String | Note | Pitch |
|---|---|---|
| 5th (short) | G | G4 |
| 4th | D | D3 |
| 3rd | G | G3 |
| 2nd | B | B3 |
| 1st | D | D4 |
Get the 4th string close to D from a piano, a reference app or a friend who owns a tuner. Then work across:
Always tune up to the note. If you overshoot, drop below and come back up, so the string settles where you leave it. And check the whole thing again at the end, because banjo heads and bridges like to shift a hair while you work.
Double C is g C G C D: lower the 4th string a whole step to C and raise the 2nd a half step to C. Popular for clawhammer tunes in C. Other common ones are G modal (g D G C D) and open D (f# D F# A D).
The Chartless tuner has banjo open G and double C as targets, so it shows how far each string is from where that tuning wants it, not just the nearest note. And once you're in tune, it'll chart the chords of whatever song is playing, drawn as banjo shapes.
More: free online tuner · banjo chord chart · dobro open G · how to tune a mandolin · all guides.