As we are only able to show the first page preview of a digital product due to publisher restriction, much of our music shows this "Voice, range:", under the Quick Details heading, to help our customers determine what transposition is right for their voice.
Let's use "Voice, range: Bb3-G5", for example.
The Bb3 in this example refers to the lowest vocal note in the arrangement and the G5 refers to the highest.
As a reference, "Middle C" is always notated as C4, so Bb3 would be the B-Flat just below Middle C and G5 would be the G just above C5 (the C that is an octave above Middle C).
Click here to learn more about voice range information as it relates to sheet music.