One important aspect of a resume is putting down range. This explanation of what really constitutes how many octaves of range was originally posted by Dancersmom, though a few additions were made.
AN EXPLANATION OF OCTAVES AND RANGE
I am going to assume that most of us understand what pitch is meant when I say middle C. The correct name for middle C is c1, pronounced "C prime" or "C one." The C that is one octave higher is c2, and the C one octave higher than that is c3. (That is the C usually referred to as the soprano's high C.) There are two octaves between middle C, or c1, and c3. The C below middle C is called small C and is written simply as c. The c one octave below that is called great C and is written as C. Great C would be an impressive pitch from a basso profundo (the very lowest male voice). (If you are confused, there is a really great representation of this on this site. This link will open in a new window.) Though there are of course more C's on a piano, labeling these is sufficient for discussion.
Just for clarification: each of these C's begins a new octave of notation. So, the D a step to the right of c1 (middle C) is labeled d1, and the B directly to the left of c2 is labeled b1.
To be as clear as possible, let's place the C's in question order beginning with the C two octaves below middle C:
C -- great C
c -- small C
c1 -- C prime, C one, middle C
c2
c3 -- soprano's high C
If a female singer's highest pitch were c3, in order to have a four octave range she would also have to be able to sing great C, the basso's pitch! She would have to be able to sing great C, small C, middle C, c2, and c3. This is five different C's for a four octave range. Most young singers do not have four octave ranges.
Therefore, in order to be able to sing X number of octaves, you must have X+1 of the same note on a different pitch. (Not necessarily C's, that is just what is used here as an example. You could sing four F's or four D's which would still qualify you for a three octave range.)
It's never a good idea to falsify a resume, so keep all this in mind when you list your range!