How you feel can indicate that you have low T (Testosterone). Symptoms include: low energy, low libido, erectile dysfunction in men, painful intercourse poor lubrication in women, decreased strength, decreased exercise endurance, decreased recovery from exercise, loss of muscle mass, increased percent body fat to lean muscle mass ratio, or depression.
The easiest method is to confirm your Testosterone levels is to consult your doctor. The most accurate measurement is to measure free and total testosterone in blood.