3 week old baby weight
On the WHO growth standard, the average (median) 3-week-old baby boy weighs 4.1 kg (8 lb 15 oz) and the average girl weighs 3.8 kg (8 lb 7 oz). The usual range, from the 3rd to the 97th percentile, is 3.1–5.2 kg for boys and 2.9–5.0 kg for girls.
Weight percentiles at 3 weeks (WHO)
The median (50th percentile) is the average weight for this age.
| 3rd | 15th | Median | 85th | 97th | |
|---|---|---|---|---|---|
| Boys (kg) | 3.10 | 3.51 | 4.06 | 4.67 | 5.22 |
| Boys (lb) | 6.8 | 7.7 | 9.0 | 10.3 | 11.5 |
| Girls (kg) | 2.92 | 3.31 | 3.84 | 4.43 | 4.96 |
| Girls (lb) | 6.4 | 7.3 | 8.5 | 9.8 | 10.9 |
Gain since birth
Going by the WHO medians, a boy gains about 714 g (1 lb 9 oz) and a girl about 603 g (1 lb 5 oz) between birth and 3 weeks.
Check your baby’s weight percentile
Enter the exact date of birth for a precise result, or use the pound table below.
Enter a date of birth and at least one measurement to see the percentile.
What percentile is my 3 week old’s weight in pounds?
WHO percentile for each weight at exactly 3 weeks. A few days older or younger shifts it slightly.
| Weight | Boy | Girl |
|---|---|---|
| 6 lb (2.72 kg) | below 1st | below 1st |
| 6 lb 8 oz (2.95 kg) | 1st | 3rd |
| 7 lb (3.18 kg) | 4th | 9th |
| 7 lb 8 oz (3.40 kg) | 10th | 20th |
| 8 lb (3.63 kg) | 21st | 35th |
| 8 lb 8 oz (3.86 kg) | 35th | 52nd |
| 9 lb (4.08 kg) | 52nd | 67th |
| 9 lb 8 oz (4.31 kg) | 67th | 80th |
| 10 lb (4.54 kg) | 79th | 89th |
| 10 lb 8 oz (4.76 kg) | 88th | 94th |
| 11 lb (4.99 kg) | 94th | 97th |
| 11 lb 8 oz (5.22 kg) | 97th | 99th |
| 12 lb (5.44 kg) | 99th | above 99th |
Length and head size at 3 weeks
WHO percentiles in cm; the median is also shown in inches.
| 3rd | 15th | Median | 85th | 97th | Median (in) | |
|---|---|---|---|---|---|---|
| Length, boys | 49.8 | 51.4 | 53.4 | 55.4 | 57.0 | 21.0 |
| Length, girls | 48.8 | 50.5 | 52.5 | 54.5 | 56.1 | 20.7 |
| Head, boys | 34.3 | 35.3 | 36.5 | 37.7 | 38.7 | 14.4 |
| Head, girls | 33.7 | 34.6 | 35.8 | 37.0 | 38.0 | 14.1 |
Common questions
How much should a 3-week-old baby weigh?
On the WHO growth standard, the average (median) 3-week-old baby boy weighs 4.1 kg (8 lb 15 oz) and the average girl weighs 3.8 kg (8 lb 7 oz). The usual range, from the 3rd to the 97th percentile, is 3.1–5.2 kg for boys and 2.9–5.0 kg for girls.
What percentile is 9 lb at 3 weeks?
On the WHO chart, 9 lb (4.1 kg) at exactly 3 weeks is about the 52nd percentile for a boy and the 67th for a girl. The table on this page gives the percentile for every half pound in the usual range.
How much weight should a baby gain by 3 weeks?
Going by the WHO medians, a boy gains about 714 g (1 lb 9 oz) between birth and 3 weeks, and a girl about 603 g (1 lb 5 oz). Individual babies vary; a steady curve over several weeks matters more than one weigh-in.
What is the average length and head size of a 3-week-old?
At 3 weeks, the WHO median length is 53.4 cm (21.0 in) for boys and 52.5 cm (20.7 in) for girls, and the median head circumference is 36.5 cm (14.4 in) for boys and 35.8 cm (14.1 in) for girls.
Is my 3-week-old underweight?
A weight between the 3rd and the 97th percentile is within the usual range, and a baby who keeps following roughly the same percentile line is growing steadily. Talk to your pediatrician if the weight is below the 3rd percentile, if your baby is not back to birth weight by about two weeks, or if the curve drops across two of the main percentile lines.
Full charts: newborn weight chart by week · length by week · head size by week · weight by month · weight gain per week
Source: WHO Child Growth Standards, expanded daily tables, at day 21. For information only; not medical advice.