Portal 2’s co-op campaign is about 5 hours long , though it can stretch longer if you and your partner explore, replay chambers, or take time solving puzzles. A broader estimate from sources around the game puts the co-op mode at 5+ hours and the campaign length at roughly six hours.

Quick take

  • Main estimate: about 5 hours.
  • More relaxed playthrough: around 5 to 6+ hours.
  • With replaying or slower puzzle solving: longer than that.

Extra context

Portal 2’s co-op is a separate campaign, so it is not just a short bonus mode. It has its own chambers and progression, which is why it lands in the same general range as a compact single-player campaign rather than a tiny side activity.

If you want, I can also give the single-player length or a campaign-by- campaign breakdown.