Average fetal length and weight chart



From early in pregnancy, babies grow at different rates, so these numbers are merely averages. Your baby's actual length and weight may vary substantially. Video
Inside pregnancy: Early fetal development 
  A 3D animated look at development of the embryo, which quickly develops from a single cell to several million cells all working together.

 Inside pregnancy: Early fetal developmentSee all videos
Don't worry too much if an ultrasound indicates that your baby is much smaller or larger. (Your practitioner will let you know if it's time to worry about how big your baby is.) By full-term, your baby may end up weighing less than 5 pounds or more than 9.

Until about 20 weeks, babies are measured from the crown (or top) of the head to the rump (or bottom). This is because a baby's legs are curled up against his torso during the first half of pregnancy and very hard to measure.

After that, babies are measured from head to toe.

See our pregnancy timing article to learn how the weeks of pregnancy are counted and your baby's gestational age is determined.





<table border="1" cellpadding="5" cellspacing="0"><tbody><tr><td><strong>Gestational age</strong></td><td><strong>Length</strong> (US)</td><td><strong>Weight</strong> (US)</td><td><strong>Length</strong> (cm)</td><td><strong>Mass</strong> (g)</td></tr><tr><td>&#160;</td><td colspan="2"><strong>(crown to rump)</strong></td><td colspan="2"><strong>(crown to rump)</strong></td></tr><tr><td><strong>8 weeks</strong></td><td>0.63 inch</td><td>0.04 ounce</td><td>1.6 cm</td><td>1 gram</td></tr><tr><td><strong>9 weeks</strong></td><td>0.90 inch</td><td>0.07 ounce</td><td>2.3 cm</td><td>2 grams</td></tr><tr><td><strong>10 weeks</strong></td><td>1.22 inch</td><td>0.14 ounce</td><td>3.1 cm</td><td>4 grams</td></tr><tr><td><strong>11 weeks</strong></td><td>1.61 inch</td><td>0.25 ounce</td><td>4.1 cm</td><td>7 grams</td></tr><tr><td><strong>12 weeks</strong></td><td>2.13 inches</td><td>0.49 ounce</td><td>5.4 cm</td><td>14 grams</td></tr><tr><td><strong>13 weeks</strong></td><td>2.91 inches</td><td>0.81 ounce</td><td>7.4 cm</td><td>23 grams</td></tr><tr><td><strong>14 weeks</strong></td><td>3.42 inches</td><td>1.52 ounce</td><td>8.7 cm</td><td>43 grams</td></tr><tr><td><strong>15 weeks</strong></td><td>3.98 inches</td><td>2.47 ounces</td><td>10.1 cm</td><td>70 grams</td></tr><tr><td><strong>16 weeks</strong></td><td>4.57 inches</td><td>3.53 ounces</td><td>11.6 cm</td><td>100 grams</td></tr><tr><td><strong>17 weeks</strong></td><td>5.12 inches</td><td>4.94 ounces</td><td>13 cm</td><td>140 grams</td></tr><tr><td><strong>18 weeks</strong></td><td>5.59 inches</td><td>6.70 ounces</td><td>14.2 cm</td><td>190 grams</td></tr><tr><td><strong>19 weeks</strong></td><td>6.02 inches</td><td>8.47 ounces</td><td>15.3 cm</td><td>240 grams</td></tr><tr><td><strong>20 weeks</strong></td><td>6.46 inches</td><td>10.58 ounces</td><td>16.4 cm</td><td>300 grams</td></tr><tr><td>&#160;</td><td colspan="2"><strong>(crown to heel)</strong></td><td colspan="2"><strong>(crown to heel)</strong></td></tr><tr><td><strong>20 weeks</strong></td><td>10.08 inches</td><td>10.58 ounces</td><td>25.6 cm</td><td>300 grams</td></tr><tr><td><strong>21 weeks</strong></td><td>10.51 inches</td><td>12.70 ounces</td><td>26.7 cm</td><td>360 grams</td></tr><tr><td><strong>22 weeks</strong></td><td>10.94 inches</td><td>15.17 ounces</td><td>27.8 cm</td><td>430 grams</td></tr><tr><td><strong>23 weeks</strong></td><td>11.38 inches</td><td>1.10 pound</td><td>28.9 cm</td><td>501 grams</td></tr><tr><td><strong>24 weeks</strong></td><td>11.81 inches</td><td>1.32 pound</td><td>30 cm</td><td>600 grams</td></tr><tr><td><strong>25 weeks</strong></td><td>13.62 inches</td><td>1.46 pound</td><td>34.6 cm</td><td>660 grams</td></tr><tr><td><strong>26 weeks</strong></td><td>14.02 inches</td><td>1.68 pound</td><td>35.6 cm</td><td>760 grams</td></tr><tr><td><strong>27 weeks</strong></td><td>14.41 inches</td><td>1.93 pound</td><td>36.6 cm</td><td>875 grams</td></tr><tr><td><strong>28 weeks</strong></td><td>14.80 inches</td><td>2.22 pounds</td><td>37.6 cm</td><td>1005 grams</td></tr><tr><td><strong>29 weeks</strong></td><td>15.2 inches</td><td>2.54 pounds</td><td>38.6 cm</td><td>1153 grams</td></tr><tr><td><strong>30 weeks</strong></td><td>15.71 inches</td><td>2.91 pounds</td><td>39.9 cm</td><td>1319 grams</td></tr><tr><td><strong>31 weeks</strong></td><td>16.18 inches</td><td>3.31 pounds</td><td>41.1 cm</td><td>1502 grams</td></tr><tr><td><strong>32 weeks</strong></td><td>16.69 inches</td><td>3.75 pounds</td><td>42.4 cm</td><td>1702 grams</td></tr><tr><td><strong>33 weeks</strong></td><td>17.20 inches</td><td>4.23 pounds</td><td>43.7 cm</td><td>1918 grams</td></tr><tr><td><strong>34 weeks</strong></td><td>17.72 inches</td><td>4.73 pounds</td><td>45 cm</td><td>2146 grams</td></tr><tr><td><strong>35 weeks</strong></td><td>18.19 inches</td><td>5.25 pounds</td><td>46.2 cm</td><td>2383 grams</td></tr><tr><td><strong>36 weeks</strong></td><td>18.66 inches</td><td>5.78 pounds</td><td>47.4 cm</td><td>2622 grams</td></tr><tr><td><strong>37 weeks</strong></td><td>19.13 inches</td><td>6.30 pounds</td><td>48.6 cm</td><td>2859 grams</td></tr><tr><td><strong>38 weeks</strong></td><td>19.61 inches</td><td>6.80 pounds</td><td>49.8 cm</td><td>3083 grams</td></tr><tr><td><strong>39 weeks</strong></td><td>19.96 inches</td><td>7.25 pounds</td><td>50.7 cm</td><td>3288 grams</td></tr><tr><td><strong>40 weeks</strong></td><td>20.16 inches</td><td>7.63 pounds</td><td>51.2 cm</td><td>3462 grams</td></tr><tr><td><strong>41 weeks</strong></td><td>20.35 inches</td><td>7.93 pounds</td><td>51.7 cm</td><td>3597 grams</td></tr><tr><td><strong>42 weeks</strong></td><td>20.28 inches</td><td>8.12 pounds</td><td>51.5 cm</td><td>3685 grams</td></tr></tbody></table>