How big is your baby during each week of pregnancy?

Fetal Growth Chart
Do you ever wonder how big your baby is at each week of pregnancy? The numbers in our chart below can give you an idea of your baby's size. Keep in mind that your baby may be much smaller or larger than these averages. That's okay – ultimately, healthy babies can weigh less than 2,200 grams or more than 4 kilograms at birth.

Boys measure differently than girls. For the numbers in our chart, we have taken an average of boys and girls. And keep in mind, height measurements up to 13 weeks are crown-to-rump estimates, while height measurements starting at 14 weeks are crown-to-heel estimates.

Gestational Age Length (cm) Weight (g) 

Crown to rump:

• 8 weeks  1.57 cm 20 grams
• 9 weeks 2.30 cm 27 grams
• 10 weeks 3.1 cm 35 grams
• 11 weeks 4.1 cm 45 grams
• 12 weeks 5.4 cm 58 grams
• 13 weeks 6.7 cm 73 grams

Crown to heel:

• 14 weeks 14.7 cm 93 grams
• 15 weeks 16.7 cm 117 grams
• 16 weeks 18.6 cm 146 grams
• 17 weeks 20.4 cm 181 grams
• 18 weeks 22.2 cm 223 grams
• 19 weeks  24.0 cm 273 grams
• 20 weeks 25.7 cm 331 grams
• 21 weeks 27.4 cm 399 grams
• 22 weeks  29.0 cm 478 grams
• 23 weeks 30.6 cm 568 grams
• 24 weeks 32.2 cm 670 grams
• 25 weeks 33.7 cm 785 grams
• 26 weeks 35.1 cm 913 grams
• 27 weeks  36.6 cm 1055 grams
• 28 weeks 37.6 cm 1210 grams
• 29 weeks 39.3 cm 1379 grams
• 30 weeks  40.5 cm 1559 grams
• 31 weeks 41.8 cm 1751 grams
• 32 weeks  43.0 cm 1953 grams
• 33 weeks  44.1 cm 2162 grams
• 34 weeks  45.3 cm 2377 grams
• 35 weeks  46.3 cm 2595 grams
• 36 weeks 47.3 cm 2813 grams
• 37 weeks 48.3 cm 3028 grams
• 38 weeks 49.3 cm 3236 grams
• 39 weeks 50.1 cm 3435 grams
• 40 weeks 51.0 cm 3619 grams
• 41 weeks  51.8 cm 3787 grams

Fetal weight by week: How does it change?
Your baby continuously gains weight during pregnancy, but not always at the same rate. If you have a single baby (not twins or more than one), your baby's growth rate accelerates until week 35, then slows down.

Here are some key points based on the estimates:

• Up to week 16, a fetus grows an average of around 19 grams per week, increasing gradually from 7 grams per week at 8 weeks to 15 grams per week at 12 weeks and 29 grams per week at week 16.
• At week 20, a fetus is gaining around 59 grams per week.
• At week 30, a fetus is gaining around 175 grams each week.
• At week 35, a fetus is gaining around 215 grams each week. At this point, their growth rate peaks.
• After 35 weeks, growth slows to around 188 grams per week. (Twins slow down earlier, at around 28 weeks, and then average around 170 grams each week.)
• In the final weeks of pregnancy, the growth rate continues to gradually slow to around 168 grams per week by week 40.

Using a measuring tape stretched across your belly, your doctor will use a fundal height measurement to check your baby's size at your prenatal visits. Starting at around 24 weeks, the measurement in centimeters should roughly correspond to your baby's gestational age. If you are 26 weeks pregnant, for example, your fundal height should be around 26 cm, give or take a centimeter in either direction.

If your doctor is concerned that your baby is very small, she will monitor your baby's size with an ultrasound, which is more accurate. Using an ultrasound, your doctor can take various measurements (head circumference and diameter, abdominal circumference, femur length) and use them to estimate your baby's size. They can also use a Doppler ultrasound to view the blood flow in your placenta.

Your baby's size by week
Here are some key points about your baby's growth during pregnancy:

At week 20, roughly halfway through pregnancy, your baby is transmitting taste signals to their brain. And you can feel it by grabbing the umbilical cord. Your baby's weight at week 20 is around 331 grams, and they are about the length of a banana.

At week 32, your baby's lungs are developing rapidly, and your baby is storing minerals like iron for the first 6 months of life. Your baby's weight at week 32 is 1.94 kilograms, and their length is around 40 cm.

At week 33, things are getting better! Your baby's skin is becoming less wrinkled, and your baby's weight at week 33 is around 3 kilograms. In length, your baby is now the size of a pineapple, around 44 cm.

At week 37, your baby's brain and lungs are still maturing, and they are still moving around a lot, regardless of how close they are. Your baby's weight at week 37 is around 3 kilograms, and they are around 48 cm long.

After your baby is born, they will be weighed and measured, and your doctor will continue to monitor their growth. While the average newborn weight is just over 3.1 kilograms, most newborns lose around 5 to 10 percent of their weight in the first few days. Don't worry – they gain it back around 2 weeks old, and by 4 months they usually double their birth weight.