Testosterone levels can be measured through blood tests, and most doctors agree that a "normal" reading falls anywhere between 300 to 1,000 nanograms per deciliter (ng/dL) for men. However, there is some debate about what constitutes low testosterone or "low T," and a low reading by itself isnt enough to warrant alarm. The best time for testing is between 7 and 10 a.m. since testosterone levels vary throughout the day. Doctors recommend getting multiple tests over the course of a couple of weeks or months to confirm a result that is lower than expected.

Normal testosterone levels vary by age and gender. For male babies who are a few months old, the normal range is between 75 and 400 ng/dL, while at age 10, the normal range is 7 to 130 ng/dL. Boys 12 or 13 years old should have a testosterone level of 7 to 800 ng/dL, while by the time they reach 15 to 16 years old, teen boys typically have a testosterone level of 100 to 1,200 ng/dL. Testosterone levels peak in the late teens, and doctors consider 300 to 1,000 ng/dL the normal range for adults 19+ years old. For women ages 19 and up, normal testosterone levels range from 15 to 70 ng/dL.

Its important to note that normal value ranges may vary slightly among different laboratories, and some labs use different measurements or test different specimens. If you feel that you may have low testosterone levels, you should see your doctor and get a test. Your doctor will look at your physical appearance and sexual development to determine if you have low testosterone levels.