Baby by Justin Bieber is in Ab at 128 beats per minute and runs 3:06 across 89 bars. It uses 6 chords — Eb, Cm, Ab, Bb, Eb5, Ebsus. The chord diagram changes as the song plays and the words light up as they are sung, so you can strum and sing along without reading ahead.
Want the melody line note by note? Baby guitar melody tab.