Which standard does this tool use?

This tool uses the WHO Child Growth Standards (2006) weight-for-age LMS tables for boys and girls aged 0–24 months. These are the international gold standard used by pediatricians worldwide.

What is a weight percentile?

A weight percentile tells you what percentage of babies of the same sex and age weigh less than your baby. For example, the 70th percentile means your baby weighs more than 70% of babies the same age and sex in the WHO reference population.

A z-score (also called a standard deviation score) measures how many standard deviations your baby's weight is above or below the median for their age and sex. A z-score of 0 equals the 50th percentile. Values between −2 and +2 are generally considered within the normal range.

What percentile range is considered healthy?

Weight-for-age percentile alone cannot determine whether a baby is healthy, underweight, or overweight. WHO uses −2 and +2 z-score cutoffs (about the 2.3rd and 97.7th percentiles) for selected indicators, but clinicians interpret serial growth and weight-for-length alongside the child's history.

Should I be concerned if my baby is below the 10th percentile?

Not necessarily — some healthy babies are naturally smaller. What matters most is a consistent growth curve over time. Consult your pediatrician if your baby crosses two major percentile lines downward between visits or if weight gain stalls.

How is the LMS method used to calculate percentile?

The LMS method uses three age-specific and sex-specific parameters: L (Box-Cox power for skewness), M (the median weight), and S (the coefficient of variation). These are used to compute a z-score with the formula z = ((weight/M)^L − 1) / (L × S), which is then converted to a percentile using the standard normal distribution.

Baby Weight Percentile Calculator

Enter your baby's sex, age in months, and weight to get their WHO weight-for-age percentile, z-score, and a full reference table.

Baby Details

Sex

Age (months, 0–24)

Use completed whole months; this tool does not interpolate fractional ages.

Weight Unit

Weight (kg)

Enter baby details on the left and click Calculate Percentile.

Reference Weight Table

WHO Child Growth Standards 2006 — weight-for-age

Percentile	Weight (kg)	Weight (lb)	Your Baby

Summary

The Baby Weight Percentile Calculator uses the WHO Child Growth Standards (2006) weight-for-age LMS parameters to compute a precise percentile and z-score for infants aged 0–24 months. It supports both kilograms and pounds, covers boys and girls separately, and displays a reference table showing the 3rd, 10th, 25th, 50th, 75th, 90th, and 97th percentile weights for the selected age and sex. All computation is client-side; no data is sent to any server. For informational use only — not a substitute for professional pediatric advice.

How it works

Select your baby's sex (male or female).
Enter the baby's age in whole months (0–24).
Choose a unit — kilograms (kg) or pounds (lb).
Enter the baby's weight and click "Calculate".
Read the percentile and z-score result.
Review the reference table to see where your baby falls across the standard percentile bands.

Use cases

Check your newborn's weight against WHO global growth standards.
Track monthly weight progress between pediatric visits.
Get a reference z-score to discuss during a clinical nutrition assessment.
Compare a baby's weight to the 3rd, 10th, 25th, 50th, 75th, 90th, and 97th percentile benchmarks.
Quickly convert between lb and kg during weigh-ins.
Identify whether weight gain is on track after illness or feeding changes.
Prepare for a pediatric appointment with precise percentile data.
Understand weight expectations month by month for a boy or girl.

Frequently Asked Questions

Last updated: 2026-09-30 · Reviewed by Nham Vu