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How to track your baby's weight and length and read WHO growth charts

Published 1 October 2026 · Dao Van Thuong · 4 min read

Record each weight, length and head measurement with the date, measured the same way each time, and look at the trend across several visits rather than at one number. On the WHO growth charts, a percentile tells you where your baby sits compared with healthy breastfed children of the same age and sex — it is a position, not a grade, and a baby who follows their own line is usually doing what they should.

This guide explains the WHO standards, how to measure and record consistently, and what to ask your doctor.

This guide is general information, not medical advice. Follow what your doctor, midwife or health visitor told you, and call emergency services in an emergency.

What are the WHO growth standards?

The WHO Child Growth Standards were built from a multi-country study of healthy children who were breastfed and raised in good conditions. They describe how young children grow when their needs are met, not just how an average population grows.

Many health systems use them for children under 2, including Vietnam's Ministry of Health and the CDC in the United States. Separate charts exist for boys and girls, and for weight-for-age, length-for-age, weight-for-length and head circumference-for-age.

What does a percentile mean?

If your baby is on the 30th percentile for weight, about 30 out of 100 healthy babies of the same age and sex in the reference group weigh less, and about 70 weigh more. That is all it means.

  • A low or high percentile is not good or bad on its own. Healthy babies sit all across the chart.
  • What doctors watch is the line over time. A baby who stays roughly on their own curve is following their pattern; a baby who crosses several percentile lines up or down is worth a closer look.
  • Some charts use z-scores or standard deviations (SD) instead of percentiles. They describe the same thing on a different scale; your doctor can explain which one your clinic uses.

How do I measure consistently?

The most reliable measurements are taken at the clinic, on calibrated scales and a measuring board. At home, you can make your own numbers more comparable:

  1. 1Weigh at a similar time of day, ideally before a feed, with the baby naked or in a dry diaper.
  2. 2Use the same scale each time. Home scales and clinic scales often disagree, so do not compare one with the other.
  3. 3Length is measured lying down for babies under 2, and needs two people to do well; leave it to the clinic if you can.
  4. 4Head circumference is measured around the widest part of the head, above the eyebrows and ears.

How should I record measurements?

Keep one table with a row per measurement: date, age, weight, length, head circumference, where it was measured, and a note (for example, “unwell this week”). Copy the numbers from the clinic's record after each visit so everything is in one place.

If you want to see the curve, ask the clinic for a printed WHO chart for your baby's sex and plot each point with a pencil. The shape is easier to read than a list of numbers.

What about babies born early?

For a baby born prematurely, doctors usually plot growth by corrected age — the age they would be if they had been born on their due date — for the first months or years, and some use charts made for preterm babies. Ask your doctor which age and chart to use, and write it at the top of your table so everyone reads the numbers the same way.

When should I talk to the doctor?

Ask your doctor if your baby's measurements cross several percentile lines, if weight stalls or drops, if your baby is feeding poorly or seems unwell, or simply if a number worries you. Short-term dips are common during illness, but the doctor is the one to judge. Bring your table to the appointment.

Where Baton helps

Baton has a growth entry for weight, length and head circumference with the date. Each measurement shows where it falls on the WHO growth standards for your baby's age and sex, as a percentile and whether it is within the usual range — a position, never a score, and not medical advice.

Growth sits in the same log as feeds, sleep and diapers. With Baton Plus you can export a PDF report for your pediatrician that includes growth entries; CSV export of every entry is free. Both parents see the same measurements through their own iCloud.