WHO growth standards
Average Baby Weight by Month
The average baby weighs about 3.2 kg (girls) to 3.3 kg (boys) at birth and roughly triples that by the first birthday: about 8.9 kg for girls and 9.6 kg for boys at 12 months (WHO medians).
Educational content only, not medical advice. Always talk to your doctor or health visitor about your child.
Average weight by month for girls and boys
| Age | Girls | Boys |
|---|---|---|
| Birth | 3.2 kg 7.1 lb | 3.3 kg 7.4 lb |
| 1 month | 4.2 kg 9.2 lb | 4.5 kg 9.8 lb |
| 2 months | 5.1 kg 11.3 lb | 5.6 kg 12.3 lb |
| 3 months | 5.8 kg 12.9 lb | 6.4 kg 14.0 lb |
| 4 months | 6.4 kg 14.2 lb | 7.0 kg 15.4 lb |
| 5 months | 6.9 kg 15.2 lb | 7.5 kg 16.6 lb |
| 6 months | 7.3 kg 16.1 lb | 7.9 kg 17.5 lb |
| 7 months | 7.6 kg 16.8 lb | 8.3 kg 18.3 lb |
| 8 months | 8.0 kg 17.5 lb | 8.6 kg 19.0 lb |
| 9 months | 8.2 kg 18.1 lb | 8.9 kg 19.6 lb |
| 10 months | 8.5 kg 18.7 lb | 9.2 kg 20.2 lb |
| 11 months | 8.7 kg 19.2 lb | 9.4 kg 20.8 lb |
| 12 months | 8.9 kg 19.7 lb | 9.6 kg 21.3 lb |
| 15 months | 9.6 kg 21.2 lb | 10.3 kg 22.7 lb |
| 18 months | 10.2 kg 22.6 lb | 10.9 kg 24.1 lb |
| 21 months | 10.9 kg 23.9 lb | 11.5 kg 25.5 lb |
| 2 years | 11.5 kg 25.3 lb | 12.1 kg 26.8 lb |
| 2 years 6 months | 12.7 kg 28.0 lb | 13.3 kg 29.3 lb |
| 3 years | 13.9 kg 30.5 lb | 14.3 kg 31.6 lb |
| 4 years | 16.1 kg 35.4 lb | 16.3 kg 36.0 lb |
| 5 years | 18.2 kg 40.2 lb | 18.3 kg 40.4 lb |
These are the middle values. Healthy babies sit anywhere between the 3rd and 97th percentile. For the full range see the charts:
How much weight does a baby gain each month?
Growth is fastest at the start. Many babies lose a little weight in the first days and are usually back to birth weight within about two weeks. After that, weight gain is quickest in the first three months, then slows down steadily through the first year. Read more in our guide to baby weight gain in the first year.
Frequently asked questions
What is the average baby weight at 6 months?
About 7.3 kg for girls and 7.9 kg for boys, the WHO 50th percentile.
Is it a problem if my baby is below average?
No. Average means the middle of a healthy range. Half of all healthy babies are below it. What matters is a steady curve over time, which your doctor checks at each visit.
Where do these numbers come from?
They are the median (50th percentile) values from the WHO Child Growth Standards, built from healthy breastfed babies in six countries.
