Uneven testicle size is usually considered normal, except if there is a swelling , pain and a discernible lump at the bigger testis, that will warrant medical attention.
The testicles of a normal adult may range from 1.57 inches (four centimeters) to 2.75 inches (seven centimeters).
One testicle, usually, the left hangs lower and a bit behind the right one.
When the room temperature is lower, when stress is present or the orgasm is reached, scrotum contracts and pulls the testicles closer to body, and opposite.