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About this tool
See average fetal length and weight for any week from 8 to 40, with a familiar fruit or vegetable comparison.
This visualizer shows the average length and weight of a fetus at any gestational week from 8 to 40, alongside the fruit or vegetable that matches that size. It reports crown-rump length (head to bottom) up to week 19 and crown-heel length (head to heel) from week 20, because those are the two different measurements pregnancy tables actually use, and mixing them is why published figures often disagree. Every number is a 50th-centile population average, not a target for your own pregnancy.
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Crown-rump and crown-heel are labelled explicitly rather than blended into one misleading length column.
Length in centimetres and inches, weight in grams or kilograms plus pounds and ounces.
The whole series is browsable, so you can see growth rates rather than a single isolated week.
The average estimated fetal weight at 28 weeks is around 1,000 g, roughly 2 lb 3 oz, with a length near 37.5 cm head to heel. Individual healthy babies vary widely around that average, which is why scans report a centile rather than a pass or fail.
Because they measure different things. Up to about week 14 scans measure crown-rump length, head to bottom, while from around week 20 the quoted figure is crown-heel, head to heel, which is several centimetres longer at the same gestation.
Roughly 150 to 230 g a week from around week 28 onwards, with the fastest gain in the mid-thirties and a slight slowing as term approaches. Average birth weight at 40 weeks is about 3.4 kg, or 7 lb 8 oz.
Not on its own. These are averages across whole populations, and scan-estimated fetal weight itself carries a margin of error of roughly 10 to 15 per cent. Your sonographer and obstetrician interpret the measurement against growth centiles and the trend across scans, which is the assessment that matters.