Baby percentile calculator
Weight, length and head circumference percentiles on the WHO growth standards, from birth to age 5. Enter any or all three, and see where your baby sits on the growth chart.
WHO is what US paediatricians use under 2. For premature babies, percentiles use corrected age until 2 years.
Enter a weight, length or head measurement to see the percentile and where it sits on the WHO curves.
What a percentile actually means
Imagine 100 healthy, breastfed six-month-old girls from the WHO study, lined up from lightest to heaviest. A baby "on the 30th percentile" is heavier than about 30 of them and lighter than about 70. Drag to pick a baby.
- The 50th isn't the "goal". The 10th and the 90th percentile are both perfectly healthy positions. Half of all healthy babies are below the median.
- Percentiles squash at the edges. Moving from the 50th to the 84th takes one standard deviation (0.95 kg here); moving from the 97th to the 99th takes much less than that. So a jump between high percentiles can mean a few grams.
- The curve matters more than the dot. Paediatricians watch whether a baby follows roughly the same line over time. Crossing two major centile lines downwards is what prompts a closer look.
How to read your baby's results
Each percentile compares your baby with healthy children of the same age and sex from the WHO Multicentre Growth Reference Study, which followed breastfed babies in Brazil, Ghana, India, Norway, Oman and the USA. Because the children in the study were raised in optimal conditions, the WHO curves describe how babies should grow, not just how they happen to grow.
Want a single measurement explained in more depth? Try the dedicated weight, length and head circumference calculators, or look up the numbers yourself in the WHO growth chart tables.
Frequently asked questions
What percentile should my baby be in?
There's no "right" percentile. Anywhere between the 3rd and 97th is considered normal on the WHO charts, and a baby who is consistently on the 10th is just as healthy as one on the 90th. What your doctor watches is whether your baby follows a similar curve over time.
Does this use WHO or CDC growth charts?
Both. It defaults to the WHO Child Growth Standards (birth to 5 years), which the CDC and the American Academy of Pediatrics recommend for all children under 2. Switch to the CDC 2000 charts for the curves US paediatricians use from age 2 up to 20 years (head circumference to 36 months).
What percentile is 9 lbs at 2 months?
On the WHO charts, 9 lb (4.08 kg) at exactly 2 months is below the 1st percentile for boys and around the 4th for girls. For a boy that is under the 3rd-percentile line and worth discussing with your paediatrician, who will look at the trend since birth. Enter your baby's exact dates above for a precise figure.
Is 27 inches tall for a 6 month old?
Yes. 27 in (68.6 cm) at 6 months is around the 67th percentile for boys and the 89th for girls on the WHO length-for-age standard: above average, and well within the normal range.
Why is my baby's weight percentile different from their length percentile?
Weight and length are measured against separate reference groups, so they rarely match. A long, lean baby might be on the 80th for length and the 40th for weight. Doctors also look at weight-for-length to see whether weight is proportional.
My baby dropped percentiles. Should I worry?
Small shifts are common, especially in the first weeks and after the first year when growth slows. Crossing two or more major centile lines (for example from the 75th to below the 25th) is the pattern that usually prompts a closer look. Measurement error at home is also common, so ask for a re-weigh at the clinic.
How do I measure my baby at home?
For weight, weigh yourself holding the baby, then yourself alone, and subtract (bathroom scales are only accurate to around 100 g). Length is best measured lying down on a flat surface with the legs gently straightened. Head circumference is the largest measurement around the head, just above the eyebrows and ears.
Data: WHO Child Growth Standards (2006) LMS tables, birth to 5 years; CDC 2000 growth charts LMS tables (cdc.gov/growthcharts), birth to 20 years. Percentiles are computed with the LMS method: z = ((X/M)^L − 1) / (L·S). The CDC recommends the WHO standards for all US children under 2.