Testicles are considered big when they exceed about 25 to 30 milliliters in volume, roughly the size of a large walnut or small egg. In fertile adult men, normal testicular volume ranges from about 17 to 50 milliliters, so there’s a wide spectrum of what qualifies as healthy. Anything consistently above 30 milliliters per testicle is formally classified as macroorchidism, meaning the testicle is larger than the standard upper range.
What Counts as Normal Size
Adult testicles typically measure between 17 and 25 milliliters each, with the average sitting around 20 to 25 milliliters. In length, that translates to roughly 4 to 4.5 centimeters along the longest axis. It’s also completely normal for one testicle to be slightly larger than the other, and the left one usually hangs a bit lower.
Doctors measure testicular volume using a tool called an orchidometer: a string of oval beads ranging from 1 to 25 milliliters. The bead that most closely matches the size of the testicle gives the reading. Ultrasound provides a more precise measurement when needed.
In studies of fertile men without any testicular conditions, the average right testicle measured about 25 milliliters and the left about 23 milliliters. So if you’re at or above those numbers, you’re on the larger side of normal but not outside the expected range.
When Big Becomes Medically Notable
A volume greater than 30 milliliters is generally considered macroorchidism. Some medical sources set the bar even higher, defining it as testicles exceeding twice the normal adult volume (so above 50 milliliters). At that point, the enlargement typically has an identifiable cause rather than just being natural variation.
The enlargement in macroorchidism comes from actual changes in testicular tissue, specifically an increase in the length and sometimes diameter of the tiny tubes inside the testicle where sperm are produced. This is different from swelling caused by fluid buildup or enlarged veins, which can make the scrotum feel bigger without the testicle itself being larger.
Why Some Testicles Are Larger
If both testicles are unusually large, the cause may be genetic, hormonal, or sometimes unknown. The most well-known genetic link is fragile X syndrome, a condition that affects intellectual development and physical features. Most males with fragile X develop noticeably enlarged testicles after puberty, along with other characteristics like a long face and large ears.
Hormonal causes include an underactive thyroid, overproduction of certain adrenal hormones, or rare pituitary tumors that overstimulate the testicles. About 2% of adults who seek help for fertility problems have enlarged testicles combined with low hormone levels, suggesting the size increase doesn’t always translate to better function.
If only one testicle is significantly larger, the most important thing to rule out is a tumor. Less commonly, a single testicle can grow as compensatory hypertrophy, meaning it gets bigger to pick up the slack when the other testicle is missing or damaged.
Bigger Testicles and Fertility
Testicular size does correlate with sperm production, since most of the testicle’s volume is made up of the tissue responsible for creating sperm. Fertile men in research studies averaged testicular volumes around 23 to 25 milliliters per side, while infertile men with the same conditions averaged only 17 to 19 milliliters. The sperm concentration gap was even more dramatic: fertile men produced roughly 100 to 112 million sperm per milliliter, compared to about 34 million in infertile men with smaller testicles.
That said, bigger doesn’t automatically mean more fertile. Macroorchidism from genetic or hormonal conditions can actually impair fertility despite the larger size. The tissue changes that cause the enlargement don’t always produce functional sperm. So while size is one indicator of reproductive capacity, it’s far from the whole picture.
How Testicles Grow During Puberty
Testicles go through a predictable growth pattern during puberty, and their size is one of the earliest markers that puberty has started. Before puberty, each testicle is less than 4 milliliters, smaller than a marble. A volume of 4 milliliters or a length of 2.5 centimeters signals the beginning of pubertal development, usually around ages 9 to 14.
From there, the growth follows a staged progression. In mid-puberty, volume reaches 9 to 12 milliliters. By late puberty, testicles reach 15 to 20 milliliters. Full adult size, 20 milliliters or more, marks the final stage. The entire process takes about 3 to 4 years. Boys who reach adult volumes on the higher end of the spectrum simply have more testicular tissue, which is a normal variation influenced by genetics and overall body size.
Swelling vs. Actual Enlargement
Not everything that feels like a big testicle actually is one. Two common conditions can make the scrotum feel larger without the testicle itself being oversized. A hydrocele is a painless collection of fluid around the testicle that makes it feel smooth and swollen. A varicocele is a cluster of enlarged veins, often described as feeling like a “bag of worms,” that can make one side of the scrotum heavier.
True testicular enlargement feels firm and uniform. The testicle itself is bigger, not the surrounding structures. If you notice a distinct lump, hardness in one area, a feeling of heaviness, or a dull ache in the lower abdomen or groin, those warrant attention. Lumps or swelling that persist for more than two weeks are worth getting checked, since testicular cancer, while uncommon, tends to show up as a painless lump or one-sided enlargement rather than a uniform increase in size on both sides.
How to Check Your Own Size
You can get a rough sense of your testicular volume at home. Each testicle should feel smooth, oval, and slightly firm, like a peeled hard-boiled egg. Roll it gently between your thumb and fingers. If you’re curious about actual measurements, the length of the long axis is the easiest dimension to estimate: under 3.5 centimeters is on the smaller side, 4 to 4.5 centimeters is average, and above 4.5 centimeters is larger than typical.
What matters more than raw size is consistency. A sudden change, whether an increase or decrease, is more clinically meaningful than where you fall on the size spectrum. If your testicles have always been on the larger side and feel normal, that’s almost certainly just your anatomy.