Baby Size Calculator
Slide to any week to see how big your baby is right now — to scale, and compared to everyday objects.
To scale: your baby vs. –
How baby size is measured week by week
Quick answer: Before about 20 weeks, “length” means crown-to-rump — head to bottom, since the legs are curled up. From around 20 weeks on, it switches to crown-to-heel — full length, head to toe — which is why the size chart appears to jump partway through pregnancy.
Fruit and vegetable comparisons are a fun shorthand, but they’re approximate — a “banana-sized” baby at 20 weeks and an actual banana aren’t identical shapes, just similar lengths. The numbers behind them come from standard fetal growth references used across ultrasound reports worldwide, and individual babies vary within a normal range at every week.
Average length and weight by week
| Week | Length | Weight |
|---|---|---|
| 12 | 5.4 cm | 14 g |
| 16 | 11.6 cm | 100 g |
| 20 | 25.6 cm | 300 g |
| 24 | 30 cm | 600 g |
| 28 | 37.6 cm | 1005 g |
| 32 | 42.4 cm | 1702 g |
| 36 | 47.4 cm | 2622 g |
| 40 | 51.2 cm | 3462 g |
Figures are population averages, not targets — your own ultrasound measurements are what matter for tracking your baby specifically.
Frequently asked questions
Why does the length measurement change partway through pregnancy?
Early on, babies are curled up, so length is measured crown-to-rump (head to bottom). From around 20 weeks, it switches to crown-to-heel (head to toe) since the legs can be measured too, which is why the numbers jump at that point.
Are fruit and vegetable size comparisons accurate?
They’re an approximate, fun way to visualize length, not an exact shape match. The actual centimeter and gram figures are more precise than the fruit label.
My baby measures bigger or smaller than average — is that a problem?
Not necessarily. There’s a wide normal range at every week, influenced by genetics, sex, and individual variation. Your provider tracks your baby’s own growth trend, which matters more than matching an average exactly.
Where do these size figures come from?
They’re based on standard fetal growth references commonly used in prenatal care and ultrasound reporting, reflecting typical measurements at each week of pregnancy.
Does this replace an ultrasound measurement?
No. This tool shows general averages for each week. Only an ultrasound can measure your specific baby’s actual size.