This is actually quite difficult to answer in all certainty. The reason for this is that every single person has a different level of testosterone with which they feel comfortable. And how people feel is actually what is important. If you feel that you are happy with your energy level, your motivation to get up in the morning and to perform tasks and your sex drive is good and you don’t always feel like falling asleep the minute you get home and your moods are quite predictable then your testosterone is probably in balance.
Yet, someone else could have a HIGHER level of testosterone than you who feels fine, and they could be constantly lacking in energy, in motivation to perform tasks, have low libidos and be irritable and suffer from unpredictable moods. The point is that testosterone is an individual thing, and people need certain amounts of them to be OK. Scientists have tried for years to isolate testosterone and find foolproof ways of measuring it and finding out what is right for people so that testosterone can be made safe and used properly.
A great example of how difficult it is to work out the maximum level of testosterone a body should have is the range of testosterone levels that has been accepted as OK for men and women. For women the range of normal levels is between 15 and 70 ng/dl but the acceptable levels are really between about 20 and 60 ng/dl, and for men the normal level for men is between 200 and 1200 ng/dl but the acceptable levels are between 500 and 1000 ng/dl.
The reason why you need to know what the maximum level of testosterone is because of the side effects of having too much testosterone. Too much testosterone in men can result in you getting spots on your back or your chest or maybe can result in male pattern baldness, a possible shrinkage of your testicles and a greater risk of prostate cancer being developed. It also can result in your sexual drive being elevated a little too high for comfort, which may or may not be a good thing depending on where you are and who you are with. You may also find a rise in your haemoglobin levels, which can be good, unless it goes too high.
Women who have a testosterone level above their maximum will tend to find that their voice deepens below a level they are comfortable with, and they may also find unwanted facial and body hair growing and that they are developing acne. They may also find that they are suffering from menstrual irregularities that can be annoying.