Typical fetal weight by week
The table shows the median (50th percentile) estimated fetal weight for each week from the in-utero standards published by Hadlock and colleagues in 1991 — one of the most widely used references in ultrasound. Half of healthy babies weigh more and half weigh less at each week.
| Weeks | Grams | Weeks | Grams | Weeks | Grams |
|---|---|---|---|---|---|
| 10 | 35 | 21 | 399 | 31 | 1,751 |
| 12 | 58 | 22 | 478 | 32 | 1,953 |
| 14 | 93 | 24 | 670 | 34 | 2,377 |
| 16 | 146 | 26 | 913 | 36 | 2,813 |
| 18 | 223 | 28 | 1,210 | 38 | 3,236 |
| 20 | 331 | 30 | 1,559 | 40 | 3,619 |
How fast babies grow
Weight gain accelerates through pregnancy. Around 20 weeks a baby gains roughly 60–70 grams a week; by the third trimester it is closer to 200 grams a week as fat stores build up. That is why the third trimester is when babies “fill out”.
How fetal weight is estimated
Nobody can weigh a baby before birth. On an ultrasound, the sonographer measures the head, abdomen and thigh bone, and a formula converts them into an estimated fetal weight (EFW). Your care team then plots it on a growth chart. What matters most is the pattern over several scans: a baby following its own line is usually growing well, even if it is smaller or larger than average.
When size is checked
Growth is commonly monitored by measuring the bump (fundal height) from about 24 weeks, with scans if it is smaller or larger than expected, or if there are other reasons to check. For the size of your baby at each week compared with fruit, see the week-by-week pages; after birth, the Baby Growth Percentile Calculator uses WHO standards.