Larger testicles generally mean higher sperm production and, in most cases, are a normal variation in anatomy. Testicular volume in healthy adults typically ranges from about 15 to 25 milliliters, roughly the size of a small plum. Where you fall in that range depends on genetics, body size, and hormonal balance. But if your testicles have recently grown larger or changed in some noticeable way, the cause matters, and some possibilities deserve prompt attention.
Testicular Size and Fertility
Most of the tissue inside a testicle is dedicated to producing sperm. Larger testicles contain more of this tissue, which is why testicular volume correlates positively with sperm count and sperm motility. A population study of young men found that those with bigger testicles also tended to have higher testosterone levels. The same study identified 18 mL as a useful cut-off for normal adult volume: below that, hormone profiles and semen quality started to look less favorable.
This doesn’t mean bigger is always better in some limitless way. Once you’re in the normal adult range, additional size doesn’t keep improving fertility in a straight line. And plenty of men with smaller-than-average testicles have no trouble with fertility at all. Size is one signal among many.
What’s Normal During Puberty
Testicles grow dramatically between childhood and adulthood, and their growth is actually the first visible sign of puberty in boys. Doctors track this using a five-stage scale. Before puberty, testicular volume sits below 4 mL. Early puberty (around ages 9 to 14) brings the testicles to about 4 to 8 mL. By mid-puberty they reach 9 to 12 mL, and by late puberty they hit 15 to 20 mL. Full adult size is 20 mL or more, though many healthy adults sit a bit below that.
If you’re a teenager or a parent noticing changes, this growth is the body’s way of ramping up hormone production. It’s completely expected and happens at different rates for different people.
Benign Reasons for Enlargement
Several harmless conditions can make one or both testicles appear larger than usual. These account for the majority of scrotal swelling and don’t typically threaten your health, though some can become uncomfortable.
- Hydrocele: A buildup of fluid around the testicle. It creates a painless, smooth swelling that can make the scrotum look noticeably bigger on one side. Hydroceles are common and often resolve without treatment, though large ones can be drained or surgically corrected.
- Varicocele: Enlarged veins within the scrotum, similar to varicose veins in the legs. These feel like a soft, irregular mass, sometimes described as a “bag of worms.” Varicoceles affect up to 15% of men and usually appear on the left side. They can sometimes affect fertility but rarely cause serious problems.
- Spermatocele: A small, fluid-filled cyst near the top of the testicle. These are painless, benign, and usually found by accident during a physical exam or self-check.
All three of these conditions change the size or feel of the scrotum without involving the testicle itself. That distinction matters when figuring out what’s going on.
Infections That Cause Swelling
Infections of the epididymis (the coiled tube behind each testicle) or the testicle itself can cause rapid, painful swelling. Epididymitis is the most common, typically affecting one side. It starts with tenderness and swelling at the back of the testicle that can spread to the entire organ. The spermatic cord often becomes tender and swollen too.
In younger, sexually active men, the usual culprits are sexually transmitted bacteria like chlamydia or gonorrhea. In older men, the infection more often traces back to urinary tract bacteria, especially in those with prostate enlargement or a recent medical procedure. Acute epididymitis lasts less than six weeks with treatment, but ignoring it risks the infection spreading and causing lasting damage.
Macro-orchidism and Genetic Conditions
Unusually large testicles that develop after puberty can be a feature of Fragile X syndrome, a genetic condition that also involves learning difficulties, a long narrow face, large ears, and a prominent jaw. Enlarged testicles (called macro-orchidism) are one of the hallmark physical features of this condition in males, becoming more apparent with age. If large testicular size appears alongside developmental or cognitive differences, genetic testing can provide a clear answer.
When Enlargement Signals Something Serious
Testicular cancer often first appears as a hard lump or area of swelling on one testicle. It can also cause a feeling of heaviness in the scrotum, a dull ache in the lower abdomen or groin, or sudden swelling. Less commonly, it triggers back pain or tenderness in breast tissue. Testicular cancer is the most common cancer in men aged 15 to 35, but it’s also one of the most treatable when caught early.
The key difference between cancer and benign swelling is texture. Cancerous lumps tend to be hard and painless, while infections are tender and inflamed, and fluid-filled conditions feel smooth and soft. But these aren’t rules you should bet on at home. Any new lump, change in shape, or unexplained swelling deserves a medical evaluation.
Testicular torsion is another urgent concern. This happens when a testicle twists on its blood supply, causing sudden, severe pain and rapid swelling. It’s a medical emergency: the testicle can be lost within hours without treatment.
How Doctors Evaluate Testicular Changes
A scrotal ultrasound is the primary tool for sorting out what’s causing enlargement. It’s painless and provides detailed images of the tissue, fluid, and blood flow inside the scrotum. Doctors can distinguish between solid masses and fluid collections, identify areas where blood flow is increased (suggesting infection) or absent (suggesting torsion or infarction), and spot cysts, enlarged veins, or suspicious growths.
In cases of infection, increased blood flow to the affected area is the hallmark finding, visible even when the tissue looks normal on the initial image. For torsion, reduced or absent blood flow is the critical signal. For cancer, a solid mass with specific patterns guides next steps.
Checking Yourself at Home
A simple self-exam helps you learn what’s normal for your body so you can spot changes early. The best time is after a warm shower, when the scrotal skin is relaxed. Stand in front of a mirror and hold your penis out of the way. Look for any visible swelling or asymmetry. Then examine each testicle individually: place your index and middle fingers underneath and your thumbs on top, and gently roll the testicle between them. You’re feeling for hard lumps, smooth bumps, or any change in size, shape, or consistency.
It’s normal for one testicle to hang slightly lower or be marginally larger than the other. You’ll also feel the epididymis as a soft, rope-like structure along the back, which is not a lump. Getting familiar with this normal anatomy is the whole point, because it makes anything new obvious.
Red Flags That Need Immediate Attention
Seek urgent care if swelling comes with severe pain (especially sudden onset), fever, nausea or vomiting, blood in your urine or semen, or pain during urination. A painless lump that you can’t explain also warrants a visit, even without other symptoms. When in doubt, err on the side of getting checked. Conditions like torsion have a narrow window for successful treatment, and testicular cancer outcomes are dramatically better with early detection.