Most electric guitars I'm familar with have something like 3-1/2 to 4 octaves. How do verbally identify them. Are the octaves numbered? For example, how would I refer to the G note on the 6th string 3rd fret as opposed to the G note on the 12th fret of the 1st string? For example, is it G1 and G4?

This came up because I was trying to figure out my vocal range and found that I can pretty much sing the notes from G on the 6th string 3rd fret to the open G on the 3rd string. I can kind of go up another octave but it's not very pretty. Soon after the open G, there's a qualitative shift in how I'm singing (like maybe it's head vs chest or something), and straining a bit and stretching my head up and out like a heron swallowing a fish. I assume this is relevent to whether or not I should use a capo for a particular song and where to place it but I'm not sure I know how. My tentative guess is that I would find the lowest and highest sung notes of the song and then transpose the key, if necessary, such that they both fall between those 2 G's.