what dotted note has the longest duration

The dotted note with the longest duration in standard notation is a dotted whole note (also called a dotted semibreve).

Why that’s the longest

• A whole note normally lasts 4 beats in common time.
• A dot adds half of the note’s original value , so a dotted whole note lasts:
  • 4 beats + 2 beats = 6 beats.
• Since the whole note is the longest basic note value used in regular notation, its dotted form (dotted whole) is the longest dotted note you will normally encounter.

If you ever see double‑dotted notes, a double‑dotted whole note would be even longer (4 + 2 + 1 = 7 beats), but in most beginner and intermediate contexts, “the dotted note with the longest duration” means the dotted whole note (6 beats).