To find out the testosterone level in the body, you would have to undergo a blood test. Also, the best time to test testosterone is in the morning between 7 and 10 AM, as that is the time when your testosterone levels are at their highest. Testosterone is measured in nano grams per deciliter (ng/dL). We have classified testosterone levels according to various stages of life. - In Children- For a new born baby and for more couple of months it should produce 75-400 ng/dL. Further till the age of 10 to 11 years it changes to 7-130 ng/dL - In Early Teens- Children between 12 to 13 years old should have 7-800 ng/dL. But as age increases, like for 15 to 16 years, it should have 100-1,200 ng/dL. - In Late Teens- Men between the age of 17 to 18 years old should have testosterone levels between 300 and 1,200 ng/dL. - In Adults-  An adult (19 years and older) should have anywhere between 240 and 950 ng/dL.