The testicles of 13-year-old boys are in the early stage of puberty, and there are no standard values for testicular size because of the large differences in individual testicular development. Usually, the testicles of 13-year-old boys are normal if they are 2.5-4 cm in diameter. If the diameter of testicles is <2.5cm or >4cm, the size of testicles may be abnormal and it is recommended to go to hospital for examination. For example, some chronic wasting diseases, endocrine disorders or hypothyroidism, pituitary gland and other diseases such as cryptorchidism may lead to small or undeveloped testes; while oversized testes are considered to have possible precocious puberty or syringomyelia, cysts, varicocele, etc. Patients need to go to pediatrics or urology for physical, estrogen six, ultrasound and other examinations, and if diseases are found to exist, then timely targeted treatment can be carried out under the guidance of doctors. If it is clear that no disease exists, but only slow or fast physical development due to physiological reasons, no special treatment is needed. You should pay attention to regular medical checkups and observation of physical signs, as well as ensure a healthy diet and moderate exercise, eat more nutritious meat, eggs, milk, vegetables and fruits, and ensure sufficient and regular sleep.