- Average weight at 12 months: girls 19 lb 12 oz (8.9 kg), boys 21 lb 4 oz (9.6 kg), the WHO median or 50th percentile.
- The usual range (3rd to 97th percentile) is 15 lb 12 oz to 25 lb for girls and 17 lb 5 oz to 26 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 12-month-old?
Type your baby's weight and we'll open the growth percentile calculator set to 12 months, with your baby's percentile, curve and a plain-words verdict. Add the real birth date there for an exact result.
12-month-old girls: weight, length and head percentiles (WHO)
| 3rd | 15th | 50th (average) | 85th | 97th | |
|---|---|---|---|---|---|
| Weight | 15 lb 12 oz 7.1 kg | 17 lb 6 oz 7.9 kg | 19 lb 12 oz 8.9 kg | 22 lb 7 oz 10.2 kg | 25 lb 11.3 kg |
| Length | 27¼ in 69.2 cm | 28 in 71.3 cm | 29¼ in 74.0 cm | 30¼ in 76.7 cm | 31 in 78.8 cm |
| Head | 16¾ in 42.3 cm | 17 in 43.5 cm | 17¾ in 44.9 cm | 18¼ in 46.3 cm | 18¾ in 47.4 cm |
12-month-old boys: weight, length and head percentiles (WHO)
| 3rd | 15th | 50th (average) | 85th | 97th | |
|---|---|---|---|---|---|
| Weight | 17 lb 5 oz 7.8 kg | 19 lb 8.6 kg | 21 lb 4 oz 9.6 kg | 23 lb 13 oz 10.8 kg | 26 lb 1 oz 11.8 kg |
| Length | 28 in 71.3 cm | 28¾ in 73.3 cm | 29¾ in 75.7 cm | 30¾ in 78.2 cm | 31½ in 80.2 cm |
| Head | 17¼ in 43.6 cm | 17½ in 44.7 cm | 18¼ in 46.1 cm | 18¾ in 47.4 cm | 19 in 48.5 cm |
WHO Child Growth Standards 2006, at exactly 12 months (day 365; 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
At one year a typical baby weighs about 2.8 (girls) to 2.9 (boys) times their birth weight, a little under the old "triples by one" rule. In length, girls have grown about 9¾ in (25 cm) and boys about 10¼ in (26 cm), roughly half their birth length. From now on growth slows a lot: about 1¾ oz (50 g) a week in the second year.
- Weight gain: about 1¾ oz (50 g) a week at this stage (WHO median).
- Since birth: 2.8 times the birth weight for girls and 2.9 for boys, and about 9¾ in (25 cm) to 10¼ in (26 cm) longer.
- Checkups: this is the age of the 12-month checkup; the next one is the 15-month checkup.
- Sleep: usually 2 naps, with 3 to 4 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 12 months with the 10-month table. The corrected age calculator works it out, and the growth calculator uses it when you add the due date.
Questions
Is 15 lb 12 oz too small for a 12-month-old girl?
That is the 3rd percentile for girls at 12 months: 3 in every 100 healthy girls weigh that or less. It isn't a diagnosis on its own. Your pediatrician looks at whether your baby has followed that line over time, how they are feeding and the parents' sizes; a curve that is falling across lines matters more than a low but steady one. For boys the 3rd percentile is 17 lb 5 oz (7.8 kg).
Do babies triple their birth weight by one year?
A little less, on the WHO standards: the typical girl weighs 2.8 times her birth weight at 12 months and the typical boy 2.9 times. The "triples by one" rule comes from older charts; a baby who doesn't quite triple is perfectly normal.
How big is the difference between boys and girls at 12 months?
On the WHO medians a boy is about 1 lb 9 oz (700 g) heavier and ¾ in (1.7 cm) longer than a girl. That is why the charts are separate: a girl on the 30th percentile and a boy on the 30th weigh different amounts.
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].