My present comfortable range is from a low G to the F above middle C= one octave and a seventh, for solid sustained tones
of 10 seconds or more.
With training, it would increase to F on the bottom, to at least a
high A natural. Possibly a tenor's B flat. It was checked by an
operatic instructor who took me through a series of warm-ups to
get me "up there". Will probably gain a few low notes over the next five years as the voice is deepening, and "lose" a half note or so at the top then, as it becomes more baritonal in tone quality.
Keep in mind though that in the (true) pop genre's, an octave and
a fifth of comfortable range is normally sufficient.
Ranges of close to two octaves are handy for "legit" singers,
like those in a leading singing role on Broadway.
A practical range of two octaves and a note (or more) is good
for the operatic singer.
Chris
P.S. Get the book, "Free Your Voice", by Roger Love.
Terrific info/exercise CD on improving your voice IMHO.