At 11 weeks of pregnancy, a fetus measures roughly 4.75 to 5.8 centimeters (about 1.5 to 2.3 inches) from crown to rump, which is the standard way size is measured this early. That’s about the size of a lime. Weight at this stage is around 0.3 ounces, or about 8 grams.
How Size Is Measured at 11 Weeks
Because a fetus this small is curled into a C-shape, measuring head to toe isn’t practical. Instead, ultrasound technicians measure crown-rump length (CRL), the distance from the top of the head to the bottom of the torso. At the start of week 11, the average CRL sits at about 47.5 millimeters. By the end of the week (11 weeks and 6 days), it reaches roughly 58 millimeters. That’s a noticeable jump in just seven days, reflecting how rapidly growth occurs during the first trimester.
Your provider uses this measurement to confirm your due date. If there’s a discrepancy between CRL and the date calculated from your last period, the ultrasound measurement is generally considered more reliable this early on.
What’s Developing at This Stage
Size is only part of the picture. At 11 weeks, the fetus is transitioning from the embryonic period into the fetal period, and a lot is happening structurally.
The skeleton is beginning to harden. Ossification centers, the spots where soft cartilage starts converting into actual bone, appear in the spine during weeks 10 and 11. By the end of week 11, ossification is underway across the cervical, thoracic, lumbar, and sacral vertebrae. The skeleton is still mostly cartilage at this point, but the framework for a bony spine is actively forming.
The toes have appeared by now, having formed around week 9, and the fingers are fully separated. Fingernails won’t develop until around week 12, but the nail beds are taking shape. The head still looks disproportionately large compared to the body, making up roughly half the total length. Facial features are becoming more defined: the ears are moving toward their final position on the sides of the head, and the eyelids are fused shut (they won’t open for months).
The Placenta Is Nearly in Charge
One of the most significant changes happening around 11 weeks isn’t about size at all. The placenta is close to taking over hormone production from the corpus luteum, the temporary structure on the ovary that has been driving pregnancy hormones since conception. By the end of week 12, the placenta fully assumes this role. This hormonal handoff is one reason many people start feeling less nauseous as the first trimester ends.
What Happens at an 11-Week Ultrasound
If you’re seeing your fetus at 11 weeks, it’s likely for a nuchal translucency (NT) scan, which is offered between 11 and 13 weeks. This screening measures a small pocket of fluid at the back of the fetus’s neck. A measurement above 3 millimeters at 12 weeks is considered elevated and usually prompts a conversation about additional testing. The scan isn’t diagnostic on its own, but combined with blood work, it helps estimate the likelihood of certain chromosomal conditions.
During this ultrasound, you can typically see the fetus moving. At 11 weeks, it can stretch, hiccup, and make small limb movements, though you won’t feel any of this for several more weeks. The heartbeat is visible and fast, usually between 120 and 160 beats per minute.
How Quickly Size Changes From Here
Growth accelerates dramatically over the next few weeks. For reference, at 8 weeks the fetus measured roughly 1.5 centimeters. At 11 weeks it’s nearly 5 centimeters. By 14 weeks, it will be close to 9 centimeters. Weight gain follows a similar curve: from a fraction of an ounce now to about 1.5 ounces by the end of the first trimester. The second trimester is when the most rapid length growth occurs, while the third trimester is when weight gain really ramps up.
Keep in mind that these numbers represent averages. Individual measurements can vary, and a CRL slightly above or below the 50th percentile at 11 weeks is completely normal. Your provider looks at the overall growth trend across multiple visits rather than any single measurement in isolation.