Free baby sleep tools
📈 Baby growth percentile calculator
Find where your baby’s measurement sits on the WHO Child Growth Standards, the charts used for babies under two in the UK Red Book and most of the world.
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WHO median weight by age
| Age | Boys (kg) | Girls (kg) |
|---|---|---|
| Newborn | 3.4 | 3.2 |
| 1 month | 4.5 | 4.2 |
| 2 months | 5.6 | 5.1 |
| 3 months | 6.4 | 5.8 |
| 4 months | 7.0 | 6.4 |
| 6 months | 7.9 | 7.3 |
| 9 months | 8.9 | 8.2 |
| 12 months | 9.7 | 8.9 |
| 15 months | 10.3 | 9.6 |
| 18 months | 10.9 | 10.2 |
| 24 months | 12.2 | 11.5 |
What a percentile means
On the 25th percentile means that out of 100 healthy babies of the same age and sex, about 25 would weigh less and 75 more. Every percentile line on the chart is healthy. What your health visitor watches is whether your baby follows roughly the same line.
Track the trend, not one number
In OBubba every measurement is plotted on the WHO curves, so you can see the line your baby follows and share it with your health visitor or GP.
Let OBubba do this for you
This chart is the average baby. OBubba learns yours.
OBubba learns your baby’s own wake windows from what you log, predicts the next nap and bedtime, and spots over 30 common sleep disruptions with a gentle plan for each. Free to download.
Questions parents ask
Frequently asked questions
Is the 10th percentile bad?
No. Any percentile can be healthy. The trend over time is what matters, along with how your baby is feeding and developing.
Which growth chart does the UK use?
The UK-WHO charts in the Personal Child Health Record (the Red Book) are based on the WHO Child Growth Standards for babies from two weeks to four years.
My baby dropped a percentile line. What should I do?
Small moves between lines are common, especially in the first weeks. If you notice a bigger change, your health visitor or GP can review it with you.
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Sleep regression checkerWhich common sleep shake-ups line up with your baby’s age, and what helps.Sources
OBubba tools give general, age-based information. They are not medical advice and do not diagnose anything. Every baby is different. If you are worried about your baby, speak to your health visitor, midwife, GP or call NHS 111 (or your local equivalent).