My testicles are 4cm long, is this normal? i feel like they should be fairly bigger then that.

Here are some ...: For adults, a 4-cm testis is on the low end of normal, but remember: the size of testes widely varies among men with its range of about 4.5-6 x 2.5-3.5 x 2.5-3.5 cm, but okay as long as functioning well in secreting testosterone and generating sperms to fulfill manhood, and having nothing unusual on personal or professional exam. More? Ask doc timely.