- Average weight at 8 months: girls 17 lb 9 oz (8.0 kg), boys 19 lb (8.6 kg), the WHO median or 50th percentile.
- The usual range (3rd to 97th percentile) is 14 lb to 22 lb 2 oz for girls and 15 lb 7 oz to 23 lb 4 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 8-month-old?
Type your baby's weight and we'll open the growth percentile calculator set to 8 months, with your baby's percentile, curve and a plain-words verdict. Add the real birth date there for an exact result.
8-month-old girls: weight, length and head percentiles (WHO)
| 3rd | 15th | 50th (average) | 85th | 97th | |
|---|---|---|---|---|---|
| Weight | 14 lb 6.3 kg | 15 lb 8 oz 7.0 kg | 17 lb 9 oz 8.0 kg | 19 lb 15 oz 9.0 kg | 22 lb 2 oz 10.0 kg |
| Length | 25¼ in 64.3 cm | 26 in 66.3 cm | 27 in 68.8 cm | 28 in 71.2 cm | 28¾ in 73.2 cm |
| Head | 16 in 40.9 cm | 16½ in 42.0 cm | 17 in 43.4 cm | 17½ in 44.8 cm | 18 in 45.9 cm |
8-month-old boys: weight, length and head percentiles (WHO)
| 3rd | 15th | 50th (average) | 85th | 97th | |
|---|---|---|---|---|---|
| Weight | 15 lb 7 oz 7.0 kg | 16 lb 15 oz 7.7 kg | 19 lb 8.6 kg | 21 lb 4 oz 9.6 kg | 23 lb 4 oz 10.6 kg |
| Length | 26¼ in 66.5 cm | 27 in 68.3 cm | 27¾ in 70.6 cm | 28¾ in 72.9 cm | 29½ in 74.8 cm |
| Head | 16½ in 42.2 cm | 17 in 43.2 cm | 17½ in 44.5 cm | 18 in 45.8 cm | 18½ in 46.9 cm |
WHO Child Growth Standards 2006, at exactly 8 months (day 244; 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 8 months most babies are on the move, and weight often grows in steps rather than smoothly: a quiet few weeks, then a jump. Look at the trend over two or three months instead of week to week. Length still grows about half an inch (1 to 1.5 cm) a month.
- 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 2.6 for boys, and about 7¾ in (20 cm) to 8¼ in (21 cm) longer.
- Next checkup: the 9-month checkup (AAP Bright Futures schedule).
- Sleep: usually 2 naps, with 2½ to 3¼ 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 8 months with the 6-month table. The corrected age calculator works it out, and the growth calculator uses it when you add the due date.
Questions
Is 14 lb too small for an 8-month-old girl?
That is the 3rd percentile for girls at 8 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 15 lb 7 oz (7.0 kg).
How much should an 8-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.
How big is the difference between boys and girls at 8 months?
On the WHO medians a boy is about 1 lb 8 oz (670 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].