Baby Size Week by Week
How big your baby is at each week of pregnancy - estimated length, weight, a size you can picture, and what is developing.
Week 20 - your baby is about the size of
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Length
-
Weight
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average
Trimester
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Weeks to go
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until week 40
What is happening this week
Average weight through pregnancy
Grams, weeks 4-40. Tap a bar to jump to that week.
4
13
22
31
40
| Week | Size | Length | Weight |
|---|
Averages, not targets. Healthy babies vary widely in size at every week. Only your own scan measurements, read by your doctor, say anything about your baby.
Frequently asked questions
How big is my baby right now?
Average length runs from about 0.1 cm at week 4 to roughly 51 cm at week 40, and weight from under a gram to around 3.4 kg. These are population averages and healthy babies vary considerably either side of them.
Why does the length jump around week 20?
Before about week 20 the legs are curled against the body, so length is measured crown to rump. From week 20 it is measured crown to heel. The figure jumps because the measurement changed, not the baby.
When will I feel the baby move?
Usually between 16 and 25 weeks. First-time mothers tend to notice movement later than those who have been pregnant before, often closer to 20-22 weeks.
When is the anomaly scan?
Typically between 18 and 22 weeks. It is a detailed ultrasound examining the baby's anatomy and organ development.