Baby size by week: how big is your baby?
See how big your baby is at every week of pregnancy, from 4 to 40 weeks: the typical length or weight, the normal range, and an everyday comparison. The numbers come from the standard reference charts used on pregnancy scans.
Don’t know your week? Find it with the gestational age calculator.
How to use it
- Find your week of pregnancy. It’s counted from the first day of your last period. If you don’t know it, the gestational age calculator works it out and shows this week’s size too.
- Move the slider to that week. Or type the week, or use the arrows to step through the weeks.
- Read the size. Up to 14 weeks you’ll see the crown-to-rump length; from 10 weeks, the typical weight and its normal range; and for every week, a rough everyday comparison.
Baby size by week chart
Length is the crown-rump length (top of the head to the bottom) used on early scans. Weight is the 50th-percentile estimated fetal weight, and the range runs from the 10th to the 90th percentile — where 80% of babies fall. The comparison is by length up to 13 weeks and by weight from 14 weeks.
| Week | About the size of | Length (crown–rump) | Weight | Typical range | Trimester |
|---|---|---|---|---|---|
| 4 weeks | a poppy seed | — | — | — | 1st |
| 5 weeks | a sesame seed | 1.9 mm | — | — | 1st |
| 6 weeks | a lentil | 5.0 mm | — | — | 1st |
| 7 weeks | a blueberry | 9.5 mm | — | — | 1st |
| 8 weeks | a raspberry | 1.6 cm (0.6 in) | — | — | 1st |
| 9 weeks | a green olive | 2.3 cm (0.9 in) | — | — | 1st |
| 10 weeks | a strawberry | 3.2 cm (1.3 in) | 35 g | 29–41 g | 1st |
| 11 weeks | a fig | 4.2 cm (1.7 in) | 45 g | 37–53 g | 1st |
| 12 weeks | a lime | 5.4 cm (2.1 in) | 58 g | 48–68 g | 1st |
| 13 weeks | a plum | 6.7 cm (2.6 in) | 73 g | 61–85 g | 1st |
| 14 weeks | a lemon | 8.2 cm (3.2 in) | 93 g | 77–109 g | 2nd |
| 15 weeks | a small apple | — | 117 g | 97–137 g | 2nd |
| 16 weeks | an orange | — | 146 g | 121–171 g | 2nd |
| 17 weeks | a pear | — | 181 g | 150–212 g | 2nd |
| 18 weeks | a sweet potato | — | 223 g | 185–261 g | 2nd |
| 19 weeks | a pomegranate | — | 273 g | 227–319 g | 2nd |
| 20 weeks | a mango | — | 331 g | 275–387 g | 2nd |
| 21 weeks | a grapefruit | — | 399 g | 331–467 g | 2nd |
| 22 weeks | a small papaya | — | 478 g | 398–559 g | 2nd |
| 23 weeks | an aubergine (eggplant) | — | 568 g | 471–665 g | 2nd |
| 24 weeks | a coconut | — | 670 g | 556–784 g | 2nd |
| 25 weeks | a small cauliflower | — | 785 g | 652–918 g | 2nd |
| 26 weeks | a small cabbage | — | 913 g | 758–1,068 g | 2nd |
| 27 weeks | a small cantaloupe | — | 1,055 g | 876–1,234 g | 2nd |
| 28 weeks | a pineapple | — | 1,210 g | 1,004–1,416 g | 3rd |
| 29 weeks | a butternut squash | — | 1,379 g | 1,145–1,613 g | 3rd |
| 30 weeks | a large cabbage | — | 1,559 g | 1,294–1,824 g | 3rd |
| 31 weeks | a small honeydew melon | — | 1,751 g | 1,453–2,049 g | 3rd |
| 32 weeks | a honeydew melon | — | 1,953 g | 1,621–2,285 g | 3rd |
| 33 weeks | a large honeydew melon | — | 2,162 g | 1,794–2,530 g | 3rd |
| 34 weeks | a small pumpkin | — | 2,377 g | 1,973–2,781 g | 3rd |
| 35 weeks | a pumpkin | — | 2,595 g | 2,154–3,036 g | 3rd |
| 36 weeks | a mini watermelon | — | 2,813 g | 2,335–3,291 g | 3rd |
| 37 weeks | a large pumpkin | — | 3,028 g | 2,513–3,543 g | 3rd |
| 38 weeks | a small watermelon | — | 3,236 g | 2,686–3,786 g | 3rd |
| 39 weeks | a small jackfruit | — | 3,435 g | 2,851–4,019 g | 3rd |
| 40 weeks | a watermelon | — | 3,619 g | 3,004–4,234 g | 3rd |
In-depth week guides: 6 weeks, 11 weeks, 13 weeks, 19 weeks and 37 weeks pregnant — or see pregnancy week by week.
How your baby’s size is measured
In the first trimester, the scan measures the crown-rump length (CRL): the straight-line length from the top of the head to the bottom. Because early growth is so predictable, CRL is also the most accurate way to date a pregnancy — the CRL calculator converts a measurement in millimetres into weeks and days. From the second trimester the baby curls up and length is hard to measure, so scans estimate weight instead, from four measurements: head width and circumference, abdominal circumference and thigh-bone (femur) length. That estimate is the EFW, the estimated fetal weight.
Size through the trimesters
By the end of the first trimester (13 weeks) the baby is about 6.7 cm (2.6 in) long and weighs roughly 73 g. At 20 weeks the typical weight is about 331 g; by 28 weeks, when the third trimester starts, it’s about 1,210 g (2 lb 11 oz); and at 40 weeks about 3,619 g (7 lb 16 oz). Most of a baby’s weight is gained in the last three months. To see which trimester you’re in by date, use the trimester calculator.
How accurate are these numbers?
They’re averages from large studies, and every baby is different. Scan estimates of weight can also be off by 10% or more in either direction. A baby measuring a little above or below the 50th percentile is entirely normal — that’s what the typical range shows. Clinicians usually look more closely when the estimated weight is below the 10th percentile (ACOG’s definition of fetal growth restriction) or above the 90th, and they put most weight on the trend across several scans rather than any single number. Twins usually measure a little smaller late in pregnancy; see the twin due date calculator.
About the fruit comparisons
Comparing the baby to a lime or a mango is a friendly way to picture size, not a measurement — fruit varies too. Up to 13 weeks we match the fruit to the baby’s length; from 14 weeks, to the typical weight, because that’s what scans track. If you want the numbers, use the length and weight columns.
Frequently asked questions
How big is the baby at 12 weeks?
At 12 weeks the baby measures about 5.4 cm (2.1 in) from crown to rump — roughly the size of a lime — and weighs around 58 g.
How big is the baby at 20 weeks?
At 20 weeks a typical estimated weight is about 331 g (11.7 oz), with most babies between 275 and 387 g — roughly the weight of a mango. That’s around the time of the mid-pregnancy anatomy scan.
How much does a baby weigh at 28 weeks?
About 1,210 g (2 lb 11 oz) on average, with a typical range of 1,004–1,416 g. Weight roughly triples between 28 weeks and term.
Why does the chart switch from length to weight?
Because that’s what scans measure. Until about 14 weeks the baby is measured from crown to rump. After that, ultrasound estimates weight from the head, abdomen and thigh-bone measurements, and estimated fetal weight is what clinicians track.
My baby is measuring small or big — should I worry?
Babies vary, and most of the time a measurement just inside or outside the typical range is normal. Clinicians usually look closer when the estimated weight is below the 10th or above the 90th percentile, and they care most about the trend across scans. Ask your care team what your result means for you.
Sources
- Hadlock FP et al. In utero analysis of fetal growth: a sonographic weight standard. Radiology 1991;181:129–133
- Robinson HP, Fleming JE. A critical evaluation of sonar “crown-rump length” measurements. Br J Obstet Gynaecol 1975
- American Family Physician (2021) — Fetal Growth Restriction Before and After Birth (ACOG and SMFM definitions)
Last meaningfully updated: 2026-10-20.