WHO Growth Standards
A plain-English guide to the growth charts pediatricians use to track how babies and young children grow — what the percentiles mean, and what they don't.
If you've ever left a check-up hearing your baby is "in the 60th percentile," that number comes from a growth standard. The most widely used one is the World Health Organization (WHO) Child Growth Standards. This article explains where they come from, what each chart measures, and how to read a percentile without reading too much into it.
This is general education, not medical advice
What are the WHO Growth Standards?
The WHO released these standards in 2006, based on the Multicentre Growth Reference Study — a project that measured roughly 8,000 healthy children across six countries (Brazil, Ghana, India, Norway, Oman, and the United States) between 1997 and 2003.
What makes them a standard rather than just a reference is the group they describe: children raised under conditions believed to support healthy growth — breastfed, well-nourished, with good healthcare and non-smoking mothers. In other words, they show how children can grow when their needs are met, not simply how an average population happens to grow.
They cover children from birth to age 5, and boys and girls have separate charts because they grow at different rates. For school-age children and teens (5–19 years), the WHO publishes a separate 2007 growth reference.
What the charts measure
Weight-for-age
- Compares your child's weight to other children the same age and sex
- The most common chart parents see at check-ups
- A low value over time can signal underweight; a doctor looks at the trend, not one reading
Length/height-for-age
- Measures how tall your child is for their age
- Length is measured lying down under age 2, standing height from age 2
- A consistently low value can indicate stunted growth worth discussing with a clinician
Weight-for-length/height
- Relates weight to body length rather than age
- Helps tell whether a child is thin or heavy for their size
- Used to spot wasting (too thin) or overweight independent of age
BMI-for-age
- Body Mass Index adjusted for a child's age and sex
- An alternative way to assess weight relative to height
- Interpreted differently for children than for adults
Head circumference-for-age
- Tracks the growth of your baby's head, which reflects brain development
- Most closely watched in the first two years
- Measured with a soft tape around the widest part of the head
Motor development milestones
- Six gross-motor milestones such as sitting, standing, and walking
- Shows the typical age window in which most children reach each one
- A companion to the size charts, focused on ability rather than measurement
Percentiles and z-scores, explained
A percentile tells you where your child sits compared to 100 children of the same age and sex. If your baby is in the 60th percentile for weight, they weigh more than 60 out of 100 children in the reference group — and less than the other 40. The 50th percentile is simply the median, the middle of the pack.
Clinicians often use z-scores (also called standard deviations, or SD) for the same idea with more precision. A z-score of 0 is the median; −2 and +2 mark the edges of the typical range. The WHO cut-offs below are written in z-scores.
A high or low percentile is not a grade
The cut-offs clinicians watch for
The WHO defines specific thresholds to flag children who may need support. These are screening signals, not diagnoses — a value past a cut-off is a reason for a professional to look closer, nothing more.
WHO standards vs. other charts
You may notice your provider uses more than one chart. Many countries adopted the WHO standards as the default for young children, and some health authorities recommend using WHO charts for children under 2 and a national reference (such as the CDC charts in the United States) from age 2 onward. The exact choice depends on where you live, so the percentile you're quoted always depends on which chart it came from.
Why this sits in your Lova journey
Lova follows your whole reproductive story — through pregnancy, postpartum, and beyond. Understanding growth standards helps you make sense of those early well-baby visits. Anything you note about this stage stays in your encrypted database on your device; we never see it.