Baby Size by Week: Fruit Comparisons and Real Measurements
Reviewed by Safi Allah Khan
Medically reviewed by: Safi Allah Khan · Written by the Momi team · Last updated 20 October 2026
Quick answer: Baby size by week grows from about 1 mm at 4 weeks, a poppy seed, to about 51 cm (20 in) and 3.4 kg (7.6 lb) at 40 weeks, a small pumpkin. Before about 20 weeks, length is measured crown to rump; after that, head to heel, so the numbers jump. All sizes are averages; healthy babies vary.
Below is the full table with fruit comparisons, centimetres and inches, grams and pounds, then what the comparisons do and don't mean and how your scan measures your baby. For week-by-week development, see pregnancy week by week.
Baby size by week: the table
Weeks are counted from the first day of your last period. Sizes are typical averages from standard fetal growth references, in line with the milestones ACOG and Mayo Clinic describe. In weeks 1 to 3 there's no baby to measure yet: week 1 is your period, conception happens around the end of week 2, and implantation in week 3.
| Week | About the size of | Length | Weight | Measured |
|---|---|---|---|---|
| 4 | a poppy seed | 1 mm (0.04 in) | – | crown to rump |
| 5 | a sesame seed | 2 mm (0.08 in) | – | crown to rump |
| 6 | a lentil | 4–6 mm (0.2 in) | – | crown to rump |
| 7 | a blueberry | 1 cm (0.4 in) | – | crown to rump |
| 8 | a raspberry | 1.6 cm (0.6 in) | – | crown to rump |
| 9 | a grape | 2.3 cm (0.9 in) | – | crown to rump |
| 10 | a kumquat | 3.1 cm (1.2 in) | 4 g (0.1 oz) | crown to rump |
| 11 | a fig | 4.1 cm (1.6 in) | 7 g (0.25 oz) | crown to rump |
| 12 | a lime | 5.4 cm (2.1 in) | 14 g (0.5 oz) | crown to rump |
| 13 | a lemon | 7.4 cm (2.9 in) | 23 g (0.8 oz) | crown to rump |
| 14 | a nectarine | 8.7 cm (3.4 in) | 43 g (1.5 oz) | crown to rump |
| 15 | an apple | 10 cm (4 in) | 70 g (2.5 oz) | crown to rump |
| 16 | an avocado | 11.6 cm (4.6 in) | 100 g (3.5 oz) | crown to rump |
| 17 | a pear | 13 cm (5.1 in) | 140 g (5 oz) | crown to rump |
| 18 | a bell pepper | 14.2 cm (5.6 in) | 190 g (6.7 oz) | crown to rump |
| 19 | a mango | 15.3 cm (6 in) | 240 g (8.5 oz) | crown to rump |
| 20 | a banana | 25 cm (10 in) | 300 g (10.6 oz) | head to heel |
| 21 | a carrot | 26.7 cm (10.5 in) | 360 g (12.7 oz) | head to heel |
| 22 | a papaya | 27.8 cm (10.9 in) | 430 g (15 oz) | head to heel |
| 23 | a grapefruit | 28.9 cm (11.4 in) | 500 g (1.1 lb) | head to heel |
| 24 | an ear of corn | 30 cm (11.8 in) | 600 g (1.3 lb) | head to heel |
| 25 | a rutabaga (swede) | 34.6 cm (13.6 in) | 660 g (1.5 lb) | head to heel |
| 26 | a head of lettuce | 35.6 cm (14 in) | 760 g (1.7 lb) | head to heel |
| 27 | a cauliflower | 36.6 cm (14.4 in) | 875 g (1.9 lb) | head to heel |
| 28 | an eggplant (aubergine) | 37.6 cm (14.8 in) | 1 kg (2.2 lb) | head to heel |
| 29 | a butternut squash | 38.6 cm (15.2 in) | 1.15 kg (2.5 lb) | head to heel |
| 30 | a cabbage | 39.9 cm (15.7 in) | 1.3 kg (2.9 lb) | head to heel |
| 31 | a coconut | 41.1 cm (16.2 in) | 1.5 kg (3.3 lb) | head to heel |
| 32 | a squash | 42.4 cm (16.7 in) | 1.7 kg (3.75 lb) | head to heel |
| 33 | a pineapple | 43.7 cm (17.2 in) | 1.9 kg (4.2 lb) | head to heel |
| 34 | a cantaloupe melon | 45 cm (17.7 in) | 2.1 kg (4.7 lb) | head to heel |
| 35 | a honeydew melon | 46.2 cm (18.2 in) | 2.4 kg (5.3 lb) | head to heel |
| 36 | a romaine lettuce | 47.4 cm (18.7 in) | 2.6 kg (5.8 lb) | head to heel |
| 37 | a bunch of Swiss chard | 48.6 cm (19.1 in) | 2.9 kg (6.3 lb) | head to heel |
| 38 | a leek | 49.8 cm (19.6 in) | 3.1 kg (6.8 lb) | head to heel |
| 39 | a small watermelon | 50.7 cm (20 in) | 3.3 kg (7.3 lb) | head to heel |
| 40 | a small pumpkin | 51.2 cm (20.2 in) | 3.4 kg (7.6 lb) | head to heel |
Weight is listed from week 10, when it's large enough to quote. Before then the embryo weighs less than a few grams.
Why the numbers jump at 20 weeks
Look at weeks 19 and 20: length goes from about 15 cm to about 25 cm in one week. Your baby didn't grow 10 cm overnight. The measurement changed:
| Measurement | What it measures | Used for |
|---|---|---|
| Crown–rump length (CRL) | Top of the head to the bottom, with the baby curled up | First-trimester dating scans and charts up to about 19 weeks |
| Crown–heel length | Top of the head to the heels, legs included | Charts from about 20 weeks, and birth length |
The NHS dating scan at about 10 to 14 weeks uses CRL to work out how far along you are, because babies grow at a very similar rate in the first trimester.
Why fruit comparisons are approximate
Fruit and vegetable comparisons make tiny numbers easier to picture: "a lime" means more than "5.4 cm" to most people. But:
- Fruit vary. A mango can be twice the size of another mango.
- Apps choose different fruit. One app's "avocado" week is another's "pear". Neither is wrong.
- Shape differs. A banana is long and thin; a baby at 20 weeks is not.
- Babies vary. Genetics, the placenta and your health all affect growth. A baby can be healthy and measure ahead or behind the average.
Some apps and charts use animals, car parts or other objects instead. They're all ways of saying the same thing. Use the centimetre and gram columns for the actual numbers, and your scan report for your own baby.
How a scan measures your baby
On later scans, a sonographer usually measures several parts of the baby and plots them on a growth chart:
- Head circumference (HC) and biparietal diameter (BPD): the size of the head
- Abdominal circumference (AC): the size of the tummy, which reflects growth and stores
- Femur length (FL): the length of the thigh bone
- Estimated fetal weight (EFW): calculated from those measurements
EFW is an estimate with a margin of error that tends to be larger late in pregnancy. That's why one measurement on its own doesn't mean much; providers look at the trend over time. ACOG notes that ultrasound exams later in pregnancy are used to check growth and the baby's well-being.
What actually affects your baby's size
- Accurate dating. If your due date is off, your baby will seem too big or too small. See can your due date change?.
- Genetics. Taller parents tend to have longer babies.
- The placenta, which delivers oxygen and nutrients.
- Your health, including blood pressure, diabetes and smoking.
- Twins and multiples, who are usually smaller than single babies at the same week.
If growth needs a closer look, your provider may offer extra growth scans. Keep feeling for your baby's movements in the third trimester and call your maternity unit if they slow down or change.
Sizes at a glance by trimester
| Milestone | Typical size |
|---|---|
| End of first trimester (13 weeks) | About 7.4 cm (2.9 in), 23 g |
| Halfway (20 weeks) | About 25 cm (10 in) head to heel, 300 g |
| Start of third trimester (28 weeks) | About 37.6 cm (14.8 in), 1 kg (2.2 lb) |
| Full term (39 weeks) | About 50.7 cm (20 in), 3.3 kg (7.3 lb) |
ACOG's own figures are close to these: about 2 inches by the end of week 12, about 12 inches by the end of week 24, nearly 15 inches and 2.5 pounds by the end of week 28, and about 20 inches and 7.5 to 8 pounds at 40 weeks.
See your baby's size in Momi
Momi follows your pregnancy week by week from your due date. The home screen shows a progress ring with the weeks to go and this week's size comparison, with approximate length and weight, and each week explains what's developing. You can save your scan pictures next to each week in the bump photo journal.
Download Momi free on the App Store or Google Play. Free with ads; optional Premium.
Related: pregnancy week by week chart · 12 weeks pregnant · 24 weeks pregnant · How Many Weeks Pregnant Am I?
Sources
- ACOG, Changes During Pregnancy (infographic)
- Mayo Clinic, Fetal development: The first trimester
- Mayo Clinic, Fetal development: The 2nd trimester
- Mayo Clinic, Fetal development: The 3rd trimester
- NHS, 12-week scan
- ACOG, Ultrasound Exams
Medical disclaimer: Momi and this website provide general information, not medical advice. Always talk to your doctor or midwife; in an emergency call your local emergency number.
FAQ
How big is my baby this week?
Find your week in the table above. For example, at 12 weeks a typical baby is about 5.4 cm (2.1 in) long, the size of a lime; at 24 weeks about 30 cm (11.8 in) and 600 g (1.3 lb); at 40 weeks about 51 cm (20 in) and 3.4 kg (7.6 lb). These are averages.
Why does the baby's length jump at 20 weeks?
Because the way it's measured changes. Until about 20 weeks, babies are curled up, so length is measured from the top of the head to the bottom (crown to rump). From about 20 weeks, many charts switch to head-to-heel length, which adds the legs.
Are fruit size comparisons accurate?
Only roughly. Fruit vary in size, and so do babies. The comparisons are meant to help you picture your baby, not to measure them. For real numbers, use the centimetre and gram columns, and for your own baby, your scan report.
What if my baby measures bigger or smaller than the chart?
Healthy babies vary, and scan measurements have a margin of error, especially later in pregnancy. Your midwife or doctor compares your baby's measurements with growth charts over time. If growth needs a closer look, they'll arrange extra checks or scans.
What is baby size by week in mm in early pregnancy?
Early on, babies are measured in millimetres. Typical crown-to-rump lengths are about 1 mm at 4 weeks, 2 mm at 5 weeks, 4 to 6 mm at 6 weeks, 10 mm (1 cm) at 7 weeks, 16 mm at 8 weeks and 23 mm at 9 weeks.
Related guides
Track this in Momi
Momi is a free pregnancy tracker app for iPhone and Android that follows pregnancy week by week, estimates the due date, and keeps a pregnancy journal, weight log, kick counter and contraction timer in one place.
