- Average weight at 1 month: girls 9 lb 3 oz (4.2 kg), boys 9 lb 13 oz (4.5 kg), the WHO median or 50th percentile.
- The usual range (3rd to 97th percentile) is 7 lb 1 oz to 11 lb 13 oz for girls and 7 lb 9 oz to 12 lb 9 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 1-month-old?
Type your baby's weight and we'll open the growth percentile calculator set to 1 month, with your baby's percentile, curve and a plain-words verdict. Add the real birth date there for an exact result.
1-month-old girls: weight, length and head percentiles (WHO)
| 3rd | 15th | 50th (average) | 85th | 97th | |
|---|---|---|---|---|---|
| Weight | 7 lb 1 oz 3.2 kg | 7 lb 15 oz 3.6 kg | 9 lb 3 oz 4.2 kg | 10 lb 9 oz 4.8 kg | 11 lb 13 oz 5.4 kg |
| Length | 19¾ in 50.0 cm | 20¼ in 51.6 cm | 21 in 53.6 cm | 22 in 55.7 cm | 22½ in 57.3 cm |
| Head | 13½ in 34.3 cm | 14 in 35.3 cm | 14½ in 36.5 cm | 14¾ in 37.7 cm | 15¼ in 38.7 cm |
1-month-old boys: weight, length and head percentiles (WHO)
| 3rd | 15th | 50th (average) | 85th | 97th | |
|---|---|---|---|---|---|
| Weight | 7 lb 9 oz 3.4 kg | 8 lb 8 oz 3.9 kg | 9 lb 13 oz 4.5 kg | 11 lb 4 oz 5.1 kg | 12 lb 9 oz 5.7 kg |
| Length | 20 in 51.0 cm | 20¾ in 52.6 cm | 21½ in 54.7 cm | 22¼ in 56.7 cm | 23 in 58.3 cm |
| Head | 13¾ in 35.0 cm | 14¼ in 36.0 cm | 14¾ in 37.2 cm | 15¼ in 38.5 cm | 15½ in 39.4 cm |
WHO Child Growth Standards 2006, at exactly 1 month (day 30; 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 first month is the fastest growth of your baby's life. A typical baby has put on about 2 lb (1 kg) since birth, now that the first-days weight loss is behind them, and gains around half a pound a week. At this age the line on the chart is still settling, so one measurement means little; the 2-month checkup will show whether the curve holds.
- Weight gain: about 7 oz (200 g) for girls and 8 oz (230 g) for boys a week at this stage (WHO median).
- Since birth: 1.3 times the birth weight for girls and 1.3 for boys, and about 1¾ in (4 cm) to 2 in (5 cm) longer.
- Checkups: this is the age of the 1-month checkup; the next one is the 2-month checkup.
- Sleep: naps whenever tiredness shows, with 35 to 60 minutes 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?
A baby born 8 weeks early hasn't reached their due date yet at 1 month, so the NICU's preterm charts fit better. From the due date on, compare with babies of the same corrected age, counted from the due date. The corrected age calculator works it out, and the growth calculator uses it when you add the due date.
Questions
My 1-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, 11 lb 13 oz (5.4 kg) for girls and 12 lb 9 oz (5.7 kg) for boys at 1 month. 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 1-month-old gain per week?
Around 7 oz (200 g) for girls and 8 oz (230 g) for boys 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).
Spotted a mistake or an outdated figure? Write to [email protected].