- Average weight at 9 months: girls 18 lb 2 oz (8.2 kg), boys 19 lb 10 oz (8.9 kg), the WHO median or 50th percentile.
- The usual range (3rd to 97th percentile) is 14 lb 8 oz to 22 lb 14 oz for girls and 15 lb 15 oz to 24 lb 1 oz for boys.
- The curve matters more than the number. A baby who keeps following roughly the same line is growing well, wherever that line is.
- Born early? Use the corrected age until 2 years.
What percentile is my 9-month-old?
Type your baby's weight and we'll open the growth percentile calculator set to 9 months, with your baby's percentile, curve and a plain-words verdict. Add the real birth date there for an exact result.
9-month-old girls: weight, length and head percentiles (WHO)
| 3rd | 15th | 50th (average) | 85th | 97th | |
|---|---|---|---|---|---|
| Weight | 14 lb 8 oz 6.6 kg | 16 lb 7.3 kg | 18 lb 2 oz 8.2 kg | 20 lb 10 oz 9.3 kg | 22 lb 14 oz 10.4 kg |
| Length | 25¾ in 65.6 cm | 26¾ in 67.6 cm | 27½ in 70.1 cm | 28½ in 72.7 cm | 29½ in 74.7 cm |
| Head | 16¼ in 41.3 cm | 16¾ in 42.4 cm | 17¼ in 43.8 cm | 17¾ in 45.2 cm | 18¼ in 46.3 cm |
9-month-old boys: weight, length and head percentiles (WHO)
| 3rd | 15th | 50th (average) | 85th | 97th | |
|---|---|---|---|---|---|
| Weight | 15 lb 15 oz 7.2 kg | 17 lb 8 oz 7.9 kg | 19 lb 10 oz 8.9 kg | 21 lb 15 oz 10.0 kg | 24 lb 1 oz 10.9 kg |
| Length | 26¾ in 67.8 cm | 27½ in 69.6 cm | 28¼ in 72.0 cm | 29¼ in 74.3 cm | 30 in 76.2 cm |
| Head | 16¾ in 42.6 cm | 17¼ in 43.7 cm | 17¾ in 45.0 cm | 18¼ in 46.3 cm | 18¾ in 47.4 cm |
WHO Child Growth Standards 2006, at exactly 9 months (day 274; one month = 30.4375 days). Length is measured lying down until 2 years. The bold column is the median; the 15th to 85th percentiles hold the middle 70% of babies.
What's typical at this age
The 9-month checkup includes a developmental screening, and your pediatrician will plot weight, length and head on the same charts as here. By now a typical baby weighs about 2.5 to 2.7 times their birth weight. Many 9-month-olds look leaner than at 6 months as they stretch in length faster than they gain weight.
- Weight gain: about 2¼ oz (65 g) a week at this stage (WHO median).
- Since birth: 2.5 times the birth weight for girls and 2.7 for boys, and about 8¼ in (21 cm) to 8¾ in (22 cm) longer.
- Checkups: this is the age of the 9-month checkup; the next one is the 12-month checkup.
- Sleep: usually 2 naps, with 2½ to 3½ hours awake in between. The nap planner turns that into a day.
How to read the table
A percentile compares your baby with 100 healthy babies of the same age and sex. The 15th percentile for weight means your baby is heavier than 15 of them and lighter than the other 85. It is not a grade: the 50th is the middle of the crowd, not the goal. Look at weight, length and head together; a baby on the 20th for weight and the 20th for length is simply a smaller baby in proportion.
Crossing two or more of the main lines over time, especially downward, is what pediatricians like to look into. The growth calculator tracks that for you: add each checkup and it draws the curve and tells you how many bands it has moved.
Born early?
For a premature baby, compare with babies of the same corrected age, counted from the due date, until about 2 years. A baby born 8 weeks early is compared at 9 months with the 7-month table. The corrected age calculator works it out, and the growth calculator uses it when you add the due date.
Questions
My 9-month-old is on the 90th percentile. Is that a problem?
No. One in ten healthy babies is at or above it, and big babies of tall parents often stay big. The usual range runs up to the 97th percentile, 22 lb 14 oz (10.4 kg) for girls and 24 lb 1 oz (10.9 kg) for boys at 9 months. What your pediatrician watches is the weight-for-length and whether the curve keeps its shape, not the height of the line.
How much should a 9-month-old gain per week?
Around 2¼ oz (65 g) a week is typical at this stage on the WHO standards. Week-to-week numbers jump with feeds, diapers and the scale, so compare over a month. Add two measurements to the growth calculator and it shows your baby's own weekly gain next to the typical one.
Which growth chart does my pediatrician use?
In the US, the CDC and the American Academy of Pediatrics recommend the WHO growth charts from birth to 2 years, the same ones as on this page, and the CDC charts from age 2. So the percentile you see here should match your pediatrician's for a baby under 2, give or take the rounding of a home scale.
Sources
- World Health Organization, WHO Child Growth Standards (2006): the weight-for-age, length-for-age and head-circumference-for-age tables. The numbers on this page come from the LMS tables in the WHO anthro package.
- CDC, Recommended growth charts (WHO charts from birth to 2, CDC charts from 2).
- American Academy of Pediatrics, Bright Futures periodicity schedule (checkup ages and screenings).
- Paruthi S. et al., Recommended amount of sleep for pediatric populations, American Academy of Sleep Medicine consensus, endorsed by the AAP (J Clin Sleep Med, 2016).
Spotted a mistake or an outdated figure? Write to [email protected].