- Average weight at 4 months: girls 14 lb 3 oz (6.4 kg), boys 15 lb 7 oz (7.0 kg), the WHO median or 50th percentile.
- The usual range (3rd to 97th percentile) is 11 lb 4 oz to 17 lb 14 oz for girls and 12 lb 7 oz to 19 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 4-month-old?
Type your baby's weight and we'll open the growth percentile calculator set to 4 months, with your baby's percentile, curve and a plain-words verdict. Add the real birth date there for an exact result.
4-month-old girls: weight, length and head percentiles (WHO)
| 3rd | 15th | 50th (average) | 85th | 97th | |
|---|---|---|---|---|---|
| Weight | 11 lb 4 oz 5.1 kg | 12 lb 7 oz 5.7 kg | 14 lb 3 oz 6.4 kg | 16 lb 2 oz 7.3 kg | 17 lb 14 oz 8.1 kg |
| Length | 22¾ in 58.0 cm | 23½ in 59.9 cm | 24½ in 62.1 cm | 25¼ in 64.3 cm | 26 in 66.2 cm |
| Head | 15 in 38.2 cm | 15½ in 39.3 cm | 16 in 40.6 cm | 16½ in 41.9 cm | 17 in 43.0 cm |
4-month-old boys: weight, length and head percentiles (WHO)
| 3rd | 15th | 50th (average) | 85th | 97th | |
|---|---|---|---|---|---|
| Weight | 12 lb 7 oz 5.6 kg | 13 lb 12 oz 6.2 kg | 15 lb 7 oz 7.0 kg | 17 lb 6 oz 7.9 kg | 19 lb 1 oz 8.6 kg |
| Length | 23½ in 60.0 cm | 24¼ in 61.7 cm | 25¼ in 63.9 cm | 26 in 66.1 cm | 26¾ in 67.8 cm |
| Head | 15½ in 39.4 cm | 16 in 40.4 cm | 16½ in 41.6 cm | 17 in 42.9 cm | 17¼ in 43.9 cm |
WHO Child Growth Standards 2006, at exactly 4 months (day 122; 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
By 4 months a typical baby has doubled their birth weight (girls 2.0 times, boys 2.1 times on the WHO medians). Weight gain slows to about 4 oz a week, which is normal and nothing to fix. Sleep often changes around now too; the nap schedule planner shows what's typical for this age.
- Weight gain: about 4 oz (110 to 120 g) a week at this stage (WHO median).
- Since birth: 2.0 times the birth weight for girls and 2.1 for boys, and about 5 in (13 cm) to 5½ in (14 cm) longer.
- Checkups: this is the age of the 4-month checkup; the next one is the 6-month checkup.
- Sleep: usually 3–4 naps, with 1½ to 2½ 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 4 months with the 2-month table. The corrected age calculator works it out, and the growth calculator uses it when you add the due date.
Questions
Is 11 lb 4 oz too small for a 4-month-old girl?
That is the 3rd percentile for girls at 4 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 12 lb 7 oz (5.6 kg).
How much should a 4-month-old gain per week?
Around 4 oz (110 to 120 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.
How big is the difference between boys and girls at 4 months?
On the WHO medians a boy is about 1 lb 4 oz (580 g) heavier and ¾ in (1.8 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].