At 11 weeks, a fetus measures roughly 42 to 52 millimeters from head to rump, which is about 1.6 to 2 inches long. That’s close to the size of a lime or a large strawberry. Growth happens quickly during this window: the fetus gains nearly a millimeter per day throughout week 11.
How Size Is Measured at 11 Weeks
Doctors measure early fetal size using something called crown-rump length (CRL), which is the distance from the top of the head to the bottom of the torso. Legs aren’t included because they’re tucked up and difficult to measure consistently. At the start of week 11 (11 weeks, 0 days), the average CRL is about 42 mm. By the end of the week (11 weeks, 6 days), it reaches around 52 mm. This measurement is the most reliable way to confirm gestational age during the first trimester, and it’s what your ultrasound technician will capture if you have a scan around this time.
Weight is harder to pin down this early. The fetus weighs roughly 7 to 10 grams, which is about a third of an ounce. The NIH’s Fetal Growth Study provides estimated fetal weight calculations starting at 10 weeks, but at this stage the numbers are so small that even slight measurement differences can shift the estimate. Your provider likely won’t focus on weight until the second trimester, when the fetus is large enough for more precise readings.
What the Fetus Looks Like at 11 Weeks
By week 11, the fetus is starting to look distinctly human. The head is still large relative to the body, making up roughly half the total length, but the body is catching up. The fingers and toes are separating from the webbed shape they had in earlier weeks, and tiny fingernails are forming. Miniature ears are taking shape on the sides of the head, though they haven’t yet moved to their final position.
Facial features are becoming more defined. The eyes have moved closer together toward the front of the face, the nasal passages are open, and a tongue and palate are present inside the mouth. Tooth buds are developing beneath the gum line, even though teeth won’t appear until months after birth.
Organ Development at This Stage
Week 11 sits near the end of the first trimester, and several key organs have hit important milestones. The diaphragm, the muscle responsible for breathing, is fully formed by 10 weeks of gestation, so it’s already in place. The liver is producing red blood cells. The kidneys are beginning to make urine, which contributes to the amniotic fluid. The intestines, which temporarily grew into the umbilical cord because there wasn’t enough room in the abdomen, are starting to migrate back into the body cavity.
The heart has been beating since around week 6, and by week 11 it’s pumping blood through an increasingly complex network of vessels. All four chambers are formed. Bone tissue is beginning to harden in some areas, replacing the softer cartilage framework that was laid down earlier. This process, called ossification, will continue throughout pregnancy and well into childhood.
Movement You Can See but Not Feel
If you have an ultrasound at 11 weeks, you may be surprised by how active the fetus is. It’s kicking, stretching, and even doing somersaults. Some parents see their baby waving tiny hands on screen. These movements are constant, but you won’t feel any of them yet. The fetus is still too small, and there’s too much cushioning from amniotic fluid. Most people start to notice fetal movement between 16 and 25 weeks, with first-time pregnancies tending toward the later end of that range.
What Happens at an 11-Week Ultrasound
Many people have their first detailed ultrasound between 11 and 14 weeks. Beyond confirming the baby’s size and heartbeat, this scan often includes a nuchal translucency measurement. The technician measures a small pocket of fluid at the back of the fetus’s neck. A measurement up to about 3 mm is considered low risk for certain genetic conditions, including Down syndrome. A thicker measurement doesn’t mean something is wrong on its own, but it may prompt additional testing. The nuchal fold naturally gets slightly thicker as the fetus grows, so the measurement is always interpreted alongside the exact gestational age.
Crown-rump length taken during this scan is also used to confirm or adjust your due date. If there’s a discrepancy between your estimated due date based on your last period and the size of the fetus, the ultrasound measurement is generally considered more accurate at this stage.
How Quickly Growth Happens From Here
The pace of growth during weeks 11 through 14 is remarkable. By week 12, the fetus will be about 6 centimeters long, and by week 14 it will have roughly doubled its current length. Weight gain accelerates even faster: the fetus will go from around 7 grams now to about 45 grams by the end of week 14. The second trimester brings a shift from forming new organs to growing and refining the ones already in place, and that’s when size increases become more dramatic week to week.