Baby Growth Percentile Calculator (WHO)

Enter the weight, length or height and, if you like, head circumference of a baby or child under 5 to see where they stand among children of the same age and sex on the World Health Organization (WHO) Child Growth Standards, as a z-score and percentile.

Last updated: 28 Oct 2026

Weight-for-age percentile49.4z-score -0.01 · girl, 6 months, 0 days

Weight z-score-0.01
Weight: WHO definitionOutside WHO’s growth-problem definitions
Length/height percentile (recumbent length)48.2
Length/height z-score-0.05
Length/height: WHO definitionOutside WHO’s growth-problem definitions
Age6 months, 0 days
Age (days)184 days

WHO growth standards (LMS): WHO 28 Oct 2026

WHO z-score lines at this age 2

How it is calculated

The WHO Child Growth Standards were published in 2006. They are based on 8440 healthy children, breastfed and living in conditions that do not constrain growth, measured in the Multicentre Growth Reference Study (MGRS) in Brazil, Ghana, India, Norway, Oman and the USA between 1997 and 2003. They describe how children should grow. The tool uses WHO’s official daily LMS tables: the rows of selected days are taken unchanged and the days in between are interpolated linearly, the days are chosen so that between the −3 and +3 SD lines the z-score never differs from WHO’s daily table by more than 0.004 on any day, or the percentile by more than 0.05 points; beyond ±3 SD (including the restricted LMS for weight, up to ±5 SD) the difference is at most 0.006 z. The result table shows the −3, −2, median, +2 and +3 z-score lines at the child’s age. WHO’s training course defines the lines this way: a child whose length/height-for-age is below −2 is “stunted”, below −3 “severely stunted”; weight-for-age below −2 is “underweight”, below −3 “severely underweight”. Above +1 for weight, WHO says there may be a growth problem, better assessed by weight-for-length/height or BMI; above +3 for height it calls the child very tall and notes this is rarely a problem. These definitions are not a diagnosis: a physician assesses growth from the trend on the chart.

Formulaz = ((measurement / M)^L − 1) / (L × S) · percentile = 100 × Φ(z)L, M, S: the Box-Cox power, median and coefficient of variation at the child’s age (in days) in the WHO table; Φ: the standard normal distribution function. For length/height and head circumference L = 1 and the formula becomes (measurement − M) / (S × M). For weight WHO uses a “restricted LMS”: above +3 or below −3 the excess is measured in the distance between the 2 and 3 SD lines at that age: z = 3 + (measurement − SD3) / (SD3 − SD2).

Find the age as the number of days between the date of birth and the measurement date (WHO’s tables are by day; 1 month = 30.4375 days).
Take that day’s L, M and S from the WHO table.
For length/height use recumbent length up to day 730 and standing height from day 731; if the child was measured the other way, add or subtract 0.7 cm.
Compute the z-score (for weight with the restricted formula beyond ±3) and the percentile from the normal distribution.
Compare the z-score with WHO’s definition lines: a value exactly on a line counts in the milder class.

Example

Say a girl born on 28 April 2026 is measured on 28 October 2026 (183 days, 6 months): 7.0 kg, 65.7 cm lying down and 42 cm head circumference. Weight comes out at z −0.35 (36.5th percentile), length at −0.02 (49.1st) and head circumference at −0.16 (43.7th). A boy born on 10 June 2024 is 870 days old that day; 0.7 cm is subtracted from his recumbent 86.0 cm to give a standing height of 85.3 cm: height z −1.67 (4.7th percentile), and at 11.2 kg weight z −1.30 (9.6th).

Frequently asked questions

What does percentile mean? Is the 30th percentile low?

The 30th percentile means 30% of children of the same age and sex are below that value and 70% above it. WHO’s growth-problem definitions are in z-scores: −2 corresponds to about the 2.3rd percentile. The 30th percentile is outside those definitions; still, your physician makes the assessment from your child’s growth trend.

What is a z-score?

It is how many standard deviations the measurement lies from the median at that age: 0 is the median, −2 is two standard deviations below it. Because weight is skewed to the right, WHO computes the z-score with the LMS method rather than a plain (measurement − median) / SD.

Should length be measured lying down or standing?

According to WHO a child under 2 is measured lying down (length) and a child of 2 or older standing (height). Standing height is on average 0.7 cm less than recumbent length; if a child under 2 was measured standing, 0.7 cm is added, and if a child of 2 or older was measured lying down, it is subtracted. Choose how the child was measured and the tool does this for you.

Do the WHO standards apply to children in Turkey?

The WHO standards were built for international use from children growing up in healthy conditions in six countries. According to WHO’s report, only about 3% of the variability in length across the six sites was due to differences between sites, against 70% due to differences between children. You can ask your physician which growth charts your child is followed on.

What about a baby born preterm?

The tool uses the calendar age (days since birth). Your physician decides how a baby born early should be assessed.

Can it be used for children over 5?

No. WHO’s 0–5 year standards run until the child has completed 60 months (day 1856). For 5–19 years WHO has a separate growth reference (2007), which is not in this tool.

Source

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