Most ovarian cysts are small, between 1 and 3 centimeters (roughly half an inch to just over an inch), and disappear on their own within a few menstrual cycles. But ovarian cysts can grow much larger. A typical range extends up to about 10 centimeters (4 inches), and in rare cases, certain types of cysts grow far beyond that, occasionally reaching the size of a watermelon or larger.
How big a cyst gets depends on what type it is, whether it’s still hormonally active, and how long it goes undetected. Understanding the size thresholds that matter can help you make sense of an ultrasound result or know what your doctor is watching for.
Normal Functional Cysts: 1 to 5 cm
The most common ovarian cysts are functional cysts, meaning they form as a normal part of your menstrual cycle. A follicle that doesn’t release its egg, or a corpus luteum that fills with fluid after ovulation, can temporarily swell into a small cyst. These are typically 1 to 3 centimeters and rarely grow beyond 7 centimeters. In premenopausal women, simple cysts under 5 centimeters almost always resolve on their own within two to three menstrual cycles without any treatment.
At this size, you probably won’t feel a thing. Most small functional cysts cause no symptoms and are only discovered incidentally during an ultrasound or pelvic exam done for another reason.
When Size Starts to Matter: 5 to 10 cm
Once a cyst reaches about 5 centimeters (2 inches), it crosses into a range where doctors pay closer attention. Cysts between 5 and 7 centimeters are generally monitored with yearly ultrasounds in premenopausal women. Cysts larger than 7 centimeters typically call for more advanced imaging or a referral to a gynecologist.
A cyst in this range is more likely to cause noticeable symptoms: a dull ache or sharp pain on one side of your lower abdomen, a sense of fullness or pressure in your belly, or bloating that doesn’t seem related to what you’ve eaten. The larger the cyst, the greater the risk of rupture, which can cause sudden, severe pain and internal bleeding. Cysts over 5 centimeters also increase the risk of ovarian torsion, where the weight of the cyst causes the ovary to twist on itself, cutting off its blood supply. Torsion is a medical emergency that requires surgery.
That said, size alone doesn’t determine whether a cyst is dangerous. A simple, fluid-filled cyst up to 10 centimeters can still be benign. The American College of Obstetricians and Gynecologists notes that simple cysts up to 10 centimeters found on ultrasound are likely benign and can be safely monitored with repeat imaging, even in postmenopausal patients. In one study of women 50 and older with simple, single-chamber cysts under 10 centimeters, nearly 70% resolved on their own, most within three months, and none turned out to be cancerous.
Beyond 10 cm: When Surgery Is Usually Recommended
A cyst larger than 10 centimeters (about 4 inches) generally warrants surgical evaluation rather than continued monitoring, especially if it has complex features on imaging like internal walls, solid areas, or irregular borders. At this size, the cyst is roughly the diameter of a grapefruit and may be visibly distending your abdomen.
Certain cyst types are more prone to reaching extreme sizes. Dermoid cysts (also called mature teratomas) contain a mix of tissue types including hair, skin, and sometimes teeth. They grow slowly in premenopausal women, averaging about 1.8 millimeters per year, but because they don’t resolve on their own, they can quietly enlarge over many years. Cystadenomas, which develop from cells on the outer surface of the ovary, can also grow very large. Mucinous cystadenomas in particular are known for reaching dramatic sizes, sometimes exceeding 30 centimeters (12 inches) or more. Case reports have documented ovarian cysts weighing over 100 pounds, though anything that extreme is exceptionally rare.
Size and Cancer Risk
A larger cyst is not automatically cancerous, but size is one factor doctors weigh alongside other ultrasound characteristics. Simple cysts, those that are thin-walled and filled only with fluid, carry a very low malignancy risk regardless of whether you’re pre- or postmenopausal. The concern rises when a cyst is “complex,” meaning it has solid components, thick walls, internal divisions, or irregular blood flow patterns.
For premenopausal women, a cyst between 2.5 and 10 centimeters with simple features can typically be watched with repeat imaging in four to six weeks. For postmenopausal women, a complex cyst over 5 centimeters generally warrants surgery regardless of blood test results, because the baseline risk of ovarian cancer is higher after menopause and the ovary is no longer producing the hormonal cycles that create and resolve functional cysts.
How Monitoring Works by Size
If a cyst is found on ultrasound, the follow-up plan depends heavily on its size, your age, and how the cyst looks on imaging.
- Under 5 cm, premenopausal: No follow-up imaging is typically needed for a simple cyst. It will most likely resolve on its own.
- 5 to 7 cm, premenopausal: Yearly ultrasound monitoring to check for growth or changes.
- Over 7 cm, premenopausal: Referral to a gynecologist for further imaging or possible surgery.
- Under 5 cm, postmenopausal: Repeat ultrasound in four to six months. If unchanged and blood markers are normal, monitoring can continue at similar intervals and may eventually be stopped.
- Over 10 cm, any age: Surgical exploration is typically recommended.
What Determines How Big a Cyst Gets
Functional cysts are self-limiting because they depend on hormonal signals that shift with each menstrual cycle. Once the hormonal trigger passes, the cyst usually shrinks and reabsorbs. This is why most functional cysts stay under 7 centimeters and disappear within a few months.
Pathological cysts, those that aren’t tied to ovulation, follow different rules. Dermoid cysts, cystadenomas, and endometriomas (cysts filled with old menstrual blood, sometimes called “chocolate cysts”) grow independently of the menstrual cycle. They won’t resolve on their own and will continue to enlarge until they’re removed or, in the case of endometriomas, until menopause slows their growth. Dermoid cysts in postmenopausal women actually tend to shrink slightly over time, losing an average of about 1.6 millimeters per year, but this doesn’t apply before menopause.
The biggest cysts on record are almost always mucinous cystadenomas that went undetected or untreated for years. Because they grow slowly and the abdomen can accommodate a surprising amount of expansion, some people attribute the gradual change to weight gain rather than seeking evaluation. By the time they’re diagnosed, these cysts can fill much of the abdominal cavity.