Comfortable notes from powerful voices

Mariah's comfortable vocal range: A2-C7 (4 Octaves, 2 notes)
Xtina's comfortable vocal range: D3-A6 (3 octaves, 4 notes)
Beyonce's comfortable vocal range: G#2-E6 (3 octaves, 4notes, 1 semitone)
Ariana's comfortable vocal range: G#3-G#6/Bb6! (3 octaves)
Demi's comfortable vocal range: Eb3-Eb6 (3 octaves)