- Average weight at 3 months: girls 12 lb 14 oz (5.8 kg), boys 14 lb 1 oz (6.4 kg), the WHO median or 50th percentile.
- The usual range (3rd to 97th percentile) is 10 lb 2 oz to 16 lb 5 oz for girls and 11 lb 3 oz to 17 lb 7 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 3-month-old?
Type your baby's weight and we'll open the growth percentile calculator set to 3 months, with your baby's percentile, curve and a plain-words verdict. Add the real birth date there for an exact result.
3-month-old girls: weight, length and head percentiles (WHO)
| 3rd | 15th | 50th (average) | 85th | 97th | |
|---|---|---|---|---|---|
| Weight | 10 lb 2 oz 4.6 kg | 11 lb 5 oz 5.1 kg | 12 lb 14 oz 5.8 kg | 14 lb 11 oz 6.7 kg | 16 lb 5 oz 7.4 kg |
| Length | 22 in 55.8 cm | 22¾ in 57.6 cm | 23½ in 59.8 cm | 24½ in 62.0 cm | 25 in 63.7 cm |
| Head | 14¾ in 37.2 cm | 15 in 38.2 cm | 15½ in 39.5 cm | 16 in 40.8 cm | 16½ in 41.9 cm |
3-month-old boys: weight, length and head percentiles (WHO)
| 3rd | 15th | 50th (average) | 85th | 97th | |
|---|---|---|---|---|---|
| Weight | 11 lb 3 oz 5.1 kg | 12 lb 7 oz 5.6 kg | 14 lb 1 oz 6.4 kg | 15 lb 13 oz 7.2 kg | 17 lb 7 oz 7.9 kg |
| Length | 22¾ in 57.6 cm | 23¼ in 59.3 cm | 24¼ in 61.4 cm | 25 in 63.5 cm | 25¾ in 65.2 cm |
| Head | 15 in 38.3 cm | 15½ in 39.3 cm | 16 in 40.5 cm | 16½ in 41.7 cm | 16¾ in 42.7 cm |
WHO Child Growth Standards 2006, at exactly 3 months (day 91; 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
Around 3 months the growth starts to slow down. A typical boy is close to doubling his birth weight (1.9 times it), and girls are not far behind (1.8). This is also when some babies begin to drift a band up or down as they leave behind the size they had in the womb and settle onto their own curve.
- Weight gain: about 4 oz (110 to 120 g) a week at this stage (WHO median).
- Since birth: 1.8 times the birth weight for girls and 1.9 for boys, and about 4¼ in (11 cm) to 4½ in (12 cm) longer.
- Next checkup: the 4-month checkup (AAP Bright Futures schedule).
- Sleep: usually 4–5 naps, with 1¼ to 2 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 3 months with the 1-month table. The corrected age calculator works it out, and the growth calculator uses it when you add the due date.
Questions
My 3-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, 16 lb 5 oz (7.4 kg) for girls and 17 lb 7 oz (7.9 kg) for boys at 3 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 3-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 3 months?
On the WHO medians a boy is about 1 lb 3 oz (530 g) heavier and ¾ in (1.6 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).
Spotted a mistake or an outdated figure? Write to [email protected].