Sperm cells are produced in the testicles, but semen is not stored there. The fluid that leaves the body during ejaculation is assembled from several different glands along the reproductive tract, and sperm cells make up only 1% to 5% of the total volume. The rest is fluid produced by glands located above and around the testicles.
What the Testicles Actually Do
The testicles have two jobs: producing sperm and producing testosterone. Inside each testicle are tightly coiled tubes called seminiferous tubules, where sperm cells are created through a process that takes roughly 64 to 72 days from start to finish. The scrotum holds the testicles slightly away from the body because sperm production requires a temperature about 3°C cooler than normal body temperature.
Once sperm cells are made, they leave the testicle almost immediately. At this point they’re immature and can’t swim. They exit through small ducts into a long, coiled tube sitting just behind each testicle called the epididymis.
Where Sperm Is Actually Stored
The epididymis is the true storage site for sperm. If you uncoiled it, this single tube would stretch about 20 feet long. Sperm spend several days traveling through it, and during that transit they undergo chemical changes that give them the ability to swim and fertilize an egg. The lower portion of the epididymis, called the tail, is where mature sperm sit and wait until ejaculation.
If sperm aren’t ejaculated, the body breaks them down and reabsorbs the cellular material. This is a normal, continuous process. The testicles don’t fill up or experience pressure from unused sperm.
What Semen Is Made Of
Semen is a mixture assembled during ejaculation, not a pre-made fluid sitting in one location. A normal ejaculation produces about 1.5 to 5 milliliters of semen, roughly a half teaspoon to a full teaspoon. Here’s where that fluid comes from:
- Seminal vesicles (65% to 75%): Two small glands near the bladder produce the majority of the fluid. This thick secretion contains fructose, which gives sperm cells energy, along with proteins and compounds that help sperm survive and move.
- Prostate gland (25% to 30%): The prostate adds a thinner, milky fluid as semen passes through the ejaculatory ducts. This fluid helps liquefy semen after ejaculation.
- Sperm from the testicles and epididymis (1% to 5%): The actual sperm cells and a small amount of accompanying fluid make up the smallest fraction of the total volume.
So the overwhelming majority of semen, over 95%, comes from glands that are nowhere near the testicles.
How Ejaculation Puts It All Together
During ejaculation, smooth muscle contractions push mature sperm from the epididymis into a tube called the vas deferens. The vas deferens carries sperm upward into the pelvic area, where it reaches a wider section called the ampulla just above the prostate. At this point, the seminal vesicles release their fluid and it mixes with the sperm. The combined mixture then passes through the ejaculatory ducts and into the urethra, picking up prostate fluid along the way. The final product exits the body as semen.
The whole assembly happens in seconds. There’s no reservoir of pre-mixed semen waiting anywhere in the body.
Vasectomy Proves the Point
A vasectomy offers a clear real-world demonstration of how little the testicles contribute to semen volume. During a vasectomy, the vas deferens is cut and sealed, which stops sperm from reaching the rest of the reproductive tract. After the procedure, the seminal vesicles and prostate still produce their fluids normally. According to the Mayo Clinic, most men notice little to no change in the amount of fluid they ejaculate. That’s because the 1% to 5% of volume that sperm contributed was never a significant portion of the total.
Why Testicle Size Doesn’t Determine Semen Volume
Because the testicles contribute so little to the final fluid, their size has minimal impact on how much semen you produce. Larger testicles may produce more sperm cells, which affects fertility, but the volume of an ejaculation depends mostly on the seminal vesicles and prostate. Factors like hydration, time since last ejaculation, and age have a bigger influence on semen volume than testicle size does.