Baby Size by Week
How big is your baby right now? Enter how many weeks pregnant you are, your due date or your last period to see a fruit-size comparison, typical length and weight, and what is developing this week, plus a full chart from week 4 to 42.
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How to use the Baby Size by Week
- Choose what you know: weeks pregnant, your due date or the first day of your last period.
- Enter the weeks and days or pick the date.
- Press Show baby size to see the fruit comparison, length and weight.
- Read the development highlights for this week and peek at next week's size.
- Scroll the chart to compare every week, or download it as CSV.
Why length is measured two ways
Early in pregnancy the baby is curled up, so ultrasound measures the crown-rump length (CRL): top of the head to the bottom. CRL is also the most accurate way to date a pregnancy, and is most reliable between about 7 and 13 weeks. From around 20 weeks, guides switch to crown-heel length, head to toe, which is why the chart appears to grow about 10 cm between weeks 19 and 20.
Baby size at a glance by trimester
| Milestone | Week | Typical length | Typical weight | Size of a… |
|---|---|---|---|---|
| Heartbeat often visible | 6 | 0.25 in (0.6 cm) | < 1 g | lentil |
| End of first trimester | 13 | 2.9 in (7.4 cm) | 0.8 oz (23 g) | lemon |
| Halfway point | 20 | 10.1 in (25.6 cm) | 10.6 oz (300 g) | banana |
| Start of third trimester | 28 | 14.8 in (37.6 cm) | 2 lb 3 oz (1,005 g) | eggplant |
| Early term | 37 | 19.1 in (48.6 cm) | 6 lb 5 oz (2,859 g) | bunch of Swiss chard |
| Due date | 40 | 20.2 in (51.2 cm) | 7 lb 10 oz (3,462 g) | small pumpkin |
Keep the comparisons in perspective
- Fruit sizes are a friendly way to picture growth, not a precise measurement. Fruits vary in size too.
- Healthy babies at full term commonly weigh anywhere from about 5 lb 8 oz to 8 lb 13 oz (2.5 to 4 kg).
- If your provider says your baby is measuring ahead or behind, they will use serial scans and your own history, not averages.
Frequently asked questions
How big is my baby at 20 weeks?
At 20 weeks a typical baby is about 10 inches (25.6 cm) long from head to heel and weighs around 10.5 ounces (300 g), roughly the length of a banana. Before 20 weeks length is usually measured from crown to rump because the legs are curled up, which is why the length seems to jump at week 20.
Where do the length and weight numbers come from?
They are typical averages compiled from fetal growth references that are widely used in pregnancy guides: crown-rump length in early pregnancy and crown-heel length from 20 weeks, with average fetal weights. Individual babies vary a lot, and your ultrasound measurements are the ones that matter for your pregnancy.
Why is my baby's ultrasound size different from this chart?
Ultrasound estimates come from measurements of the head, abdomen and thigh bone and have a margin of error of around 10 to 15 percent in later pregnancy. Genetics, the parents' size and the exact dating of the pregnancy also matter, so a difference of a week or two from an average chart is common.
Is week 12 the same as the 12th week?
No. "12 weeks pregnant" means 12 full weeks have passed since the first day of the last period, so you are in your 13th week. This tool shows sizes for completed weeks, the convention used by doctors and most pregnancy apps.
How are pregnancy weeks counted?
Pregnancy is counted from the first day of the last menstrual period (LMP), about two weeks before conception. A full-term pregnancy is about 40 weeks from LMP, or 280 days. Your due date minus 280 days gives the LMP-equivalent start date.
When does a baby gain the most weight?
Most weight is gained in the third trimester. A typical baby roughly triples in weight between 28 weeks (about 2.2 lb) and 40 weeks (about 7.6 lb), mostly as fat that helps regulate temperature after birth.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.