Why is one testicle usually bigger than the other?

Your additional details indicate you may have an hernia or hydrocele. An hernia is when your intestines descend through an opening that should have closed before you are born, down into your testicle, so youre seeing one extremely larger than the other. Have it checked asap specially if it is painful. It may indicate the hernia is incarcerated or in lay man's term, blood isn't able to flow into your intestine since it is now strangled down into your scrotum. be well.

I agree with both the other people and they are right about women and the breasts being bigger, my left is smaller then the right so you and me are both righties hahaha. You also sometimes get more fluid going to one ball (sorry if the is rude just some of my keys are broken) but that's normall unless it get horrible painful.

The chord for one testicle is longer than the right one allowing it to hang lower. It is normal, my one testicle hangs lower too.

One side of your body is larger than the other. Women have different sized breasts. Not drastic size differences, but you can somewhat notice.... unless they are fake.