- Average weight at 18 months: girls 22 lb 9 oz (10.2 kg), boys 24 lb 2 oz (10.9 kg), the WHO median or 50th percentile.
- The usual range (3rd to 97th percentile) is 18 lb to 28 lb 10 oz for girls and 19 lb 9 oz to 29 lb 11 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 18-month-old?
Type your baby's weight and we'll open the growth percentile calculator set to 18 months, with your baby's percentile, curve and a plain-words verdict. Add the real birth date there for an exact result.
18-month-old girls: weight, length and head percentiles (WHO)
| 3rd | 15th | 50th (average) | 85th | 97th | |
|---|---|---|---|---|---|
| Weight | 18 lb 8.2 kg | 19 lb 14 oz 9.0 kg | 22 lb 9 oz 10.2 kg | 25 lb 11 oz 11.7 kg | 28 lb 10 oz 13.0 kg |
| Length | 29¾ in 75.2 cm | 30½ in 77.7 cm | 31¾ in 80.7 cm | 33 in 83.7 cm | 34 in 86.2 cm |
| Head | 17¼ in 43.6 cm | 17¾ in 44.8 cm | 18¼ in 46.2 cm | 18¾ in 47.7 cm | 19¼ in 48.8 cm |
18-month-old boys: weight, length and head percentiles (WHO)
| 3rd | 15th | 50th (average) | 85th | 97th | |
|---|---|---|---|---|---|
| Weight | 19 lb 9 oz 8.9 kg | 21 lb 8 oz 9.7 kg | 24 lb 2 oz 10.9 kg | 27 lb 1 oz 12.3 kg | 29 lb 11 oz 13.5 kg |
| Length | 30½ in 77.2 cm | 31¼ in 79.5 cm | 32½ in 82.3 cm | 33½ in 85.1 cm | 34½ in 87.3 cm |
| Head | 17¾ in 44.9 cm | 18 in 46.0 cm | 18¾ in 47.4 cm | 19¼ in 48.7 cm | 19¾ in 49.9 cm |
WHO Child Growth Standards 2006, at exactly 18 months (day 548; 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 18-month checkup includes developmental and autism screening, along with weight, length and head. Toddlers this age gain only about 1¾ oz (50 g) a week and often look leaner as they walk and run. A toddler who sits on the same line as at 12 months is growing exactly as expected.
- Weight gain: about 1¾ oz (50 g) a week at this stage (WHO median).
- Since birth: 3.2 times the birth weight for girls and 3.3 for boys, and about 12½ in (32 cm) to 12¾ in (32 cm) longer.
- Checkups: this is the age of the 18-month checkup; the next one is the 2-year checkup.
- Sleep: usually 1 nap, with 5 to 6 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 18 months with 16-month-old babies. The corrected age calculator works it out, and the growth calculator uses it when you add the due date.
Questions
My 18-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, 28 lb 10 oz (13.0 kg) for girls and 29 lb 11 oz (13.5 kg) for boys at 18 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 an 18-month-old gain per week?
Around 1¾ oz (50 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].