There are no hard and fast rules about how long a full body workout should be. On average, it’s probably going to take somewhere between 30 minutes and 2 hours.
It all depends on how often you’re training, what your goals are, and the amount of volume your muscles need to grow.
How often are you training?
Most people using full-body workouts for the purposes of building muscle are lifting weights 2-3 days a week. In this case, an effective workout will last somewhere between 45 minutes and 2 hours.
However, if you’re training more often (4-5 days a week), you can spread the same amount of work across more training sessions. As a result, each workout won’t last as long.
For example, let’s say that you’re lifting weights twice a week, with each workout lasting a total of one hour, making for a total of two hours of training each week.
But if you were to add an extra couple of workouts, so that you’re training four days a week, the length of each session can be reduced. The same amount of work is now being spread across four workouts rather than two, making each workout shorter.
How quickly do you want to gain muscle?
Perhaps you’re trying to gain as much muscle as you can as quickly as possible, and you’re willing to do whatever it takes to carve out the time necessary to achieve that goal.
If so, a full body workout might last anywhere between 1-2 hours.
On the flip side, putting on muscle might be one of several goals you’re working on at the moment.
Spending 1-2 hours in the gym isn’t something you have the time for, and you’re willing to accept the fact that building the muscle you want is going to happen more slowly.
What type of training are you doing? Two people might do the same total number of sets, but one uses supersets, while the other doesn’t.
All other things being equal, the use of supersets will make for shorter workouts, even though the muscle-building stimulus generated by both training sessions will be roughly identical.
How many sets do your muscles need to grow?
Beginners tend to respond very quickly to even a small amount of resistance training, and don’t require as many sets to make their muscles grow. Because of that, they can get away with shorter workouts.
But as the weeks and months go by, your body adapts, and the gains will slow down. To continue making progress you’ll need more work. That work will typically come in the form of more sets, which in turn will make for longer workouts, or a shift to some kind of split routine.
People are also different in the sense that one person might require more sets than another to stimulate the same level of hypertrophy. As a result, they’ll need to spend longer in the gym.
To sum up, there’s no single correct amount of time that a full body workout should last.
There are so many factors to consider, from training frequency to the amount of stimulation your muscles need to grow, that it’s impossible to say exactly how long a full body workout should last.
On average, it’s going to be somewhere between 30 minutes and 2 hours. For the majority of people, that will be enough to get the job done.