18 week old baby weight
On the WHO growth standard, the average (median) 18-week-old baby boy weighs 7.1 kg (15 lb 10 oz) and the average girl weighs 6.5 kg (14 lb 5 oz). The usual range, from the 3rd to the 97th percentile, is 5.7–8.7 kg for boys and 5.1–8.2 kg for girls.
Looking for 18 months? 18 month old baby weight
Weight percentiles at 18 weeks (WHO)
The median (50th percentile) is the average weight for this age.
| 3rd | 15th | Median | 85th | 97th | |
|---|---|---|---|---|---|
| Boys (kg) | 5.70 | 6.29 | 7.07 | 7.94 | 8.72 |
| Boys (lb) | 12.6 | 13.9 | 15.6 | 17.5 | 19.2 |
| Girls (kg) | 5.14 | 5.71 | 6.49 | 7.38 | 8.19 |
| Girls (lb) | 11.3 | 12.6 | 14.3 | 16.3 | 18.1 |
Gain since birth
Going by the WHO medians, a boy gains about 3727 g (8 lb 3 oz) and a girl about 3258 g (7 lb 3 oz) between birth and 18 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 18 week old’s weight in pounds?
WHO percentile for each weight at exactly 18 weeks. A few days older or younger shifts it slightly.
| Weight | Boy | Girl |
|---|---|---|
| 11 lb (4.99 kg) | below 1st | 2nd |
| 11 lb 8 oz (5.22 kg) | below 1st | 4th |
| 12 lb (5.44 kg) | 1st | 8th |
| 12 lb 8 oz (5.67 kg) | 3rd | 14th |
| 13 lb (5.90 kg) | 6th | 22nd |
| 13 lb 8 oz (6.12 kg) | 10th | 32nd |
| 14 lb (6.35 kg) | 17th | 43rd |
| 14 lb 8 oz (6.58 kg) | 26th | 54th |
| 15 lb (6.80 kg) | 37th | 65th |
| 15 lb 8 oz (7.03 kg) | 48th | 74th |
| 16 lb (7.26 kg) | 59th | 82nd |
| 16 lb 8 oz (7.48 kg) | 69th | 87th |
| 17 lb (7.71 kg) | 78th | 92nd |
| 17 lb 8 oz (7.94 kg) | 85th | 95th |
| 18 lb (8.16 kg) | 90th | 97th |
| 18 lb 8 oz (8.39 kg) | 94th | 98th |
| 19 lb (8.62 kg) | 96th | 99th |
| 19 lb 8 oz (8.85 kg) | 98th | above 99th |
Length and head size at 18 weeks
WHO percentiles in cm; the median is also shown in inches.
| 3rd | 15th | Median | 85th | 97th | Median (in) | |
|---|---|---|---|---|---|---|
| Length, boys | 60.2 | 62.0 | 64.2 | 66.3 | 68.1 | 25.3 |
| Length, girls | 58.3 | 60.1 | 62.4 | 64.6 | 66.4 | 24.6 |
| Head, boys | 39.5 | 40.5 | 41.8 | 43.0 | 44.0 | 16.4 |
| Head, girls | 38.4 | 39.4 | 40.7 | 42.0 | 43.1 | 16.0 |
Common questions
How much should an 18-week-old baby weigh?
On the WHO growth standard, the average (median) 18-week-old baby boy weighs 7.1 kg (15 lb 10 oz) and the average girl weighs 6.5 kg (14 lb 5 oz). The usual range, from the 3rd to the 97th percentile, is 5.7–8.7 kg for boys and 5.1–8.2 kg for girls.
What percentile is 15 lb at 18 weeks?
On the WHO chart, 15 lb (6.8 kg) at exactly 18 weeks is about the 37th percentile for a boy and the 65th 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 18 weeks?
Going by the WHO medians, a boy gains about 3727 g (8 lb 3 oz) between birth and 18 weeks, and a girl about 3258 g (7 lb 3 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 18-week-old?
At 18 weeks, the WHO median length is 64.2 cm (25.3 in) for boys and 62.4 cm (24.6 in) for girls, and the median head circumference is 41.8 cm (16.4 in) for boys and 40.7 cm (16.0 in) for girls.
Is my 18-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, monthly tables interpolated at day 126. For information only; not medical advice.