How long should a workout be on average?

I'd just like to know because I do workouts but I feel like they are not long enough.
Updates:
Most Helpful Guys
- Depends on intensity. You can do a 20 minute workout that is more effective than 90 minutes I see some people spending at the gym.
What Girls & Guys Said
723Related myTakes
Click "Show More" for your mentions
Most Helpful Opinion(mho) Rate.
Learn more
Learn more
Most Helpful Girls