A quarter note has a duration of one beat in common time (4/4). A dotted quarter note, on the other hand, has a duration of one and a half beats. The dot adds half the value of the note it follows, so in this case:
- A quarter note = 1 beat
- A dotted quarter note = 1 beat + 1/2 beat = 1.5 beats
Therefore, a dotted quarter note lasts longer than a quarter note by half a beat.