Pregnancy is measured in gestational age — counted from the first day of your last menstrual period (LMP), not from conception. That means at "8 weeks pregnant," the embryo itself is closer to 6 weeks old. Gestational age is always rounded down to completed weeks, so 27 weeks 6 days is still called "27 weeks."
The fruit, vegetable, and seed comparisons on this page are a visual memory aid used worldwide to help picture each stage of fetal growth — they are not a clinical measurement. The numbers that actually appear on your scan report are crown-rump length (CRL) in the first trimester, and biparietal diameter, head circumference, abdominal circumference, and femur length from the second trimester onward, used in formulas like Hadlock's to estimate fetal weight. You can run those directly with our EFW Hadlock calculator or work out your exact week from your due date with the pregnancy wheel.
1Baby Size Chart by Week — Quick Reference
A fast lookup of average fetal length and fetal weight for every week, with the matching fruit, vegetable, or seed comparison.
| Week | Looks like | Length | Weight | Trimester |
|---|---|---|---|---|
| 4 | 🟤 Poppy seed | ~2 mm | — | 1st |
| 5 | ⚪ Sesame seed | ~3 mm | — | 1st |
| 6 | 🟢 Lentil | ~0.5 cm | <1 g | 1st |
| 7 | 🫐 Blueberry | ~0.95 cm | ~1 g | 1st |
| 8 | 🫘 Kidney bean | ~1.6 cm | ~1 g | 1st |
| 9 | 🍇 Grape | ~2.3 cm | ~2 g | 1st |
| 10 | 🟠 Kumquat | ~3.1 cm | ~35 g | 1st |
| 11 | 🟣 Fig | ~4.1 cm | ~45 g | 1st |
| 12 | 🟢 Lime | ~5.4 cm | ~58 g | 1st |
| 13 | 🍋 Lemon | ~6.7 cm | ~73 g | 1st |
| 14 | 🍑 Peach | ~14.7 cm | ~93 g | 2nd |
| 15 | 🍎 Apple | ~16.7 cm | ~117 g | 2nd |
| 16 | 🥑 Avocado | ~18.6 cm | ~146 g | 2nd |
| 17 | 🍐 Pear | ~20.4 cm | ~181 g | 2nd |
| 18 | 🫑 Bell pepper | ~22.2 cm | ~223 g | 2nd |
| 19 | 🍅 Large tomato | ~24 cm | ~273 g | 2nd |
| 20 | 🍌 Banana | ~25.7 cm | ~331 g | 2nd |
| 21 | 🥕 Carrot | ~27.4 cm | ~399 g | 2nd |
| 22 | 🍈 Spaghetti squash | ~29 cm | ~478 g | 2nd |
| 23 | 🥭 Large mango | ~30.6 cm | ~568 g | 2nd |
| 24 | 🌽 Ear of corn | ~32.2 cm | ~670 g | 2nd |
| 25 | 🥬 Rutabaga | ~33.7 cm | ~785 g | 2nd |
| 26 | 🥬 Head of lettuce | ~35.1 cm | ~913 g | 2nd |
| 27 | 🥦 Cauliflower | ~36.6 cm | ~1055 g | 2nd |
| 28 | 🍆 Large eggplant | ~37.9 cm | ~1.21 kg | 3rd |
| 29 | 🎃 Butternut squash | ~39.2 cm | ~1.38 kg | 3rd |
| 30 | 🥬 Cabbage | ~40.5 cm | ~1.56 kg | 3rd |
| 31 | 🥥 Coconut | ~41.8 cm | ~1.75 kg | 3rd |
| 32 | 🥔 Jicama | ~43 cm | ~1.95 kg | 3rd |
| 33 | 🍍 Pineapple | ~44 cm | ~2.16 kg | 3rd |
| 34 | 🍈 Cantaloupe | ~45.2 cm | ~2.38 kg | 3rd |
| 35 | 🍈 Honeydew melon | ~46.3 cm | ~2.60 kg | 3rd |
| 36 | 🥬 Romaine lettuce | ~47.3 cm | ~2.81 kg | 3rd |
| 37 | 🥬 Bunch of chard | ~48.3 cm | ~3.03 kg | 3rd |
| 38 | 🥬 Leek | ~49.2 cm | ~3.24 kg | 3rd |
| 39 | 🍉 Mini watermelon | ~50.1 cm | ~3.44 kg | 3rd |
| 40 | 🎃 Small pumpkin | ~51 cm | ~3.62 kg | 3rd |
| 41 | 🍉 Small watermelon | ~51.5 cm | ~3.70 kg | Post-term |
| 42 | 🍉 Watermelon | ~51.7 cm | ~3.80 kg | Post-term |
2First Trimester — Weeks 4 to 13
Growth is tracked by crown-rump length (CRL) — top of the head to bottom of the torso, since the legs are curled and not yet measurable.
3Second Trimester — Weeks 14 to 27
From here, length is measured crown-to-heel rather than crown-to-rump, and fetal weight estimates become clinically meaningful.
4Third Trimester — Weeks 28 to 42
Growth from here is mostly about fat and muscle gain and continued brain maturation rather than new structures — weight gain accelerates noticeably.
5Is My Baby Measuring Big or Small for Dates?
- Measuring small (SGA): estimated weight below the 10th centile for gestational age. Sometimes constitutional (small parents, small baby), sometimes a sign of placental insufficiency — followed up with serial growth scans and Doppler studies.
- Measuring big (LGA): estimated weight above the 90th centile. Often linked to maternal diabetes or gestational diabetes, post-term pregnancy, or simply larger parents.
- What actually matters: the trend across two or more scans, plotted on a growth chart, tells doctors far more than any single measurement on its own.
6Twin Pregnancy: Are Twin Babies Smaller?
On average, yes — but not until later in pregnancy. Twins typically track close to singleton growth curves up to around 28–30 weeks. After that point, growth velocity in twin pregnancies tends to slow relative to single babies, mainly because two babies are sharing uterine space and placental capacity. This is why twin pregnancies are usually followed with more frequent growth scans from the late second trimester onward, and why average twin birth weight (commonly around 2.5 kg per baby) runs lower than the singleton average above.
7Premature Baby Size and Weight by Week
If a baby is born before 37 completed weeks, the average size and weight at the time of birth simply match the figures for that gestational week in the chart above — for example, a baby born at 32 weeks weighs roughly ~1.95 kg on average, around the size of a jicama. Babies born early are generally classified as:
- Extremely preterm: before 28 weeks
- Very preterm: 28–31 weeks
- Moderate to late preterm: 32–36 weeks
- Early term: 37–38 weeks
Premature babies are typically smaller for their corrected age even after birth, and pediatricians track their growth on preterm-adjusted charts until they "catch up" — usually within the first one to two years.
8How These Size Estimates Are Calculated
Two formulas do most of the work behind any baby size chart:
- Crown-rump length (CRL): used from about 6 to 13 weeks 6 days — the single most accurate way to date a pregnancy and judge early growth.
- Estimated fetal weight (EFW): from the second trimester onward, formulas such as Hadlock's combine biparietal diameter, head circumference, abdominal circumference, and femur length, typically within about ±15% of true birth weight.
Run both directly with our pregnancy wheel and EFW Hadlock calculator, or check your current week against your due date with the due date calculator.
9Frequently Asked Questions
How is pregnancy week counted when comparing baby size?
Pregnancy is dated in gestational age — counted from the first day of your last menstrual period, not from conception. So "week 8" means 8 weeks since your last period began, even though the embryo itself is only about 6 weeks old. Gestational age is always rounded down to completed weeks.
Are the fruit and vegetable size comparisons medically accurate?
They're a visual memory aid, not a clinical measurement. The figures clinicians use are crown-rump length in the first trimester, and biparietal diameter, head circumference, abdominal circumference, and femur length from the second trimester onward. Fruit comparisons just make those numbers easier to picture — they don't replace an ultrasound report.
Why is my baby's size different from the chart?
Every figure on a size chart is a population average, with a normal range of roughly ±2 standard deviations either side. A single ultrasound estimate of fetal weight also carries about ±15% measurement variability. A baby tracking consistently along their own growth curve is usually more reassuring than matching an average exactly.
Is my baby measuring big or small for dates a problem?
Not on its own. Isolated single measurements above or below the average are common and often explained by parental size, dating accuracy, or measurement technique. Doctors become more concerned when growth crosses centiles over serial scans, or when size is paired with other findings such as abnormal fluid volume or Doppler changes.
Are twin babies smaller than singleton babies?
Yes, on average — though twins track close to singleton growth curves until around 28–30 weeks. After that, growth velocity slows compared to single babies, mainly due to shared uterine space and placental capacity, which is why twin pregnancies get more frequent growth scans later on.
When can fetal weight first be estimated on ultrasound?
Crown-rump length is used for dating and size from about 6 to 13 weeks 6 days. True estimated fetal weight, using formulas such as Hadlock's, becomes clinically reliable from around 14–20 weeks onward and is most often quoted at the second-trimester anomaly scan.
What is the difference between crown-rump length and crown-heel length?
Crown-rump length (CRL) measures top of the head to bottom of the torso, used up to about 13–14 weeks before the legs can be reliably straightened for measurement. From the second trimester onward, length is reported crown-to-heel, including the legs.
⚠️ For general patient education only. This page does not replace antenatal scans, growth-chart plotting, or your obstetrician's individual assessment. Reviewed 6/27/2026 by Dr. Diamond Sharma, MBBS, AFIH (PMC Reg. 52691), Medical Officer, AAC Golewala Government Clinic, Bathinda, Punjab. Size data adapted from standard obstetric growth references (crown-rump length and Hadlock sonographic weight standards).