Prostate, seminal vesicles or testis which one is bigger(by volume and size)?
The average seminal vesicle length was 31±10.3mm and its average volume 7.1±5.2cc. That is verified by another source which states 6-10mm in controls.

The average prostate volume ranges from 20 to 40cc from ages 30  to 80, 3-2-3cm for younger males 5-4-5 for older ones.