A testosterone level is the amount of testosterone circulating in your blood, measured through a simple blood test. For adult men, the normal range is roughly 193 to 824 ng/dL (nanograms per deciliter), while the widely used clinical cutoff for low testosterone is 300 ng/dL. Women produce testosterone too, at much lower concentrations. Understanding what your number means requires knowing which type of test you got, when the blood was drawn, and how your age factors in.
What the Test Actually Measures
Testosterone travels through your bloodstream in two forms. Most of it is bound to proteins, primarily one called sex-hormone-binding globulin (SHBG) and another called albumin. A small fraction floats freely, unattached to anything. Your body can only readily use the free, unbound testosterone for tasks like building muscle and maintaining bone density. The bound portion is essentially in storage.
This distinction matters because doctors can order different versions of the test. A total testosterone test measures everything in your blood, both bound and free. A free testosterone test measures only the unattached portion. A bioavailable testosterone test captures free testosterone plus the portion loosely bound to albumin (which your body can still access relatively easily). Most initial screenings use total testosterone, but if your total number looks normal and you still have symptoms, your doctor may check free or bioavailable levels to get a more complete picture.
Normal Ranges by Age and Sex
Testosterone levels shift dramatically across a lifetime. In boys, levels stay below 12 ng/dL until around age 6, then begin climbing. During puberty (ages 11 to 15), they can surge to as high as 830 ng/dL. By ages 16 to 17, the typical range settles between 102 and 1,010 ng/dL. For adult men aged 18 and older, the standard reference range is 193 to 824 ng/dL.
Women have far lower levels, typically between about 15 and 70 ng/dL depending on age and the lab running the test. Despite the smaller amounts, testosterone plays a real role in female health, contributing to bone strength, muscle maintenance, and sex drive.
If you see your results reported in nmol/L instead of ng/dL (common outside the United States), you can convert by knowing that 20 nmol/L equals roughly 576 ng/dL.
When Levels Are Considered Low
The American Urological Association uses a total testosterone level below 300 ng/dL as the threshold supporting a diagnosis of low testosterone in men. Other medical societies worldwide set their cutoffs anywhere from 230 to 350 ng/dL, so there’s no single universal number. A result just above or below that line doesn’t automatically mean something is wrong. Doctors look at the number alongside your symptoms and often repeat the test before making any diagnosis.
Symptoms of low testosterone in men include reduced sex drive, difficulty with erections, loss of muscle size and strength, increased body fat, bone loss, fatigue, sleep problems, depression, and trouble concentrating. Some men with levels below 300 ng/dL feel perfectly fine, while others with levels technically in the “normal” range have noticeable symptoms. The number is a starting point, not the whole story.
Why Levels Decline With Age
Starting around age 40, testosterone drops by about 1 to 2% per year in men. This is a gradual, natural process, not a sudden cliff. A man with a level of 600 ng/dL at 30 might sit around 450 to 500 ng/dL by his mid-50s. The decline varies widely from person to person, and many men maintain levels well within the normal range into their 60s and 70s. Age-related decline alone doesn’t necessarily require treatment unless it’s causing significant symptoms.
Factors That Skew Your Results
A single testosterone reading can be misleading because several temporary factors influence the number. Testosterone follows a daily rhythm, peaking in the early morning and dropping through the afternoon. This is why doctors recommend getting your blood drawn in the morning for the most accurate reading. In some cases, you may also be asked to fast beforehand.
Sleep has a measurable impact. Going a full 24 hours without sleep significantly lowers testosterone levels, and 40 to 48 hours of sleep deprivation drops them even further. A bad night or two of partial sleep may not move the needle much, but chronic poor sleep can suppress your baseline over time. Chronic stress also inhibits testosterone production, so a blood draw during an unusually stressful period may not reflect your true baseline.
Underlying health conditions matter too. Obesity, type 2 diabetes, metabolic syndrome, liver disease, chronic kidney disease, and heart failure can all push testosterone levels down independently of age. Losing weight or getting a chronic condition under better control sometimes brings levels back up without any testosterone-specific treatment. Because so many variables can influence a single test, doctors typically require at least two low readings taken on separate mornings before confirming a diagnosis.
Total vs. Free: Which Number Matters More
For most people, total testosterone is the first and most useful number. It’s standardized, widely available, and forms the basis of the 300 ng/dL diagnostic cutoff. But total testosterone can sometimes be misleading. If your SHBG levels are unusually high (which can happen with aging, liver conditions, or certain medications), more of your testosterone gets locked up in binding proteins. Your total looks fine, but very little is actually available for your body to use. In that scenario, checking free testosterone gives a clearer answer.
Conversely, conditions like obesity tend to lower SHBG, which can make free testosterone appear relatively normal even when total testosterone is low. This is why some doctors order both tests together when the clinical picture doesn’t match the initial result. There’s no single perfect measurement, but understanding the difference helps you have a more informed conversation about what your numbers actually mean.