Child growth percentile calculator

The child growth calculator reads a measurement against the WHO Child Growth Standards, the reference the World Health Organization published in 2006 for children from birth to five years. Enter age in months, sex, length or height and weight, and it returns the percentile band the measurement falls in. It leads with the band rather than a single centile because it holds the published cut-offs at nine anchor ages and interpolates between them, which is enough to place a child and not enough to argue about one point.

What people use it for

Making sense of a number from a clinic

A health visitor gives a weight and a centile and it goes out of your head by the time you get home. Entering the measurement yourself puts the band back in front of you, with the reference named, so the number has a context rather than sitting alone on a card.

Checking the same measurement twice

The tool asks whether the child was measured lying down or standing, because below 24 months the WHO tables expect a length and above it a height, and the two differ by about 0.7 cm. Entering the wrong one shifts the answer, which is worth knowing before worrying about the result.

Following a direction rather than a point

A child tracking steadily along the same line is usually reassuring; a change of direction is what a clinician wants to see. Running the same calculation at a few visits shows a shape, which is the only thing a single reading cannot.

How it works

Choose the sex — The WHO publishes separate tables for girls and boys, and they differ enough that reading the wrong one gives a genuinely wrong answer.
Enter the age in whole months — Zero to 60. Past 60 months a different reference applies — the WHO Growth Reference 2007 — which this tool does not implement.
Enter length or height, and weight — Length below two years (lying down), height from two (standing). Weight without clothes or a nappy where you can.
Pick what to read it against — Weight-for-age or height-for-age. Both use the measurements you have already entered.
Read the band first — The band is what these anchor rows support. The percentile figure beside it is an approximation, and the method section says so.

Questions

My child is on a low percentile. Is that bad?

Not by itself. Somebody has to be on every line, and a child who has always tracked along the same one is usually growing exactly as expected for them. What clinicians look at is the shape over time rather than any single point. If the line changes direction, that is worth a conversation.

Why does it ask whether the child is a girl or a boy?

Because the WHO publishes separate tables, and they differ enough that reading the wrong one gives a genuinely wrong answer. It is not used for anything else, and it is not stored unless you save the reading to your record.

Can I use this for a baby born early?

Not reliably. Premature babies are normally plotted against corrected age — age from the due date rather than the birth date — and this tool does not apply that correction. Your neonatal or paediatric team will have the right chart.

How exact is the percentile?

It is an approximation, and the page says so rather than hiding it. The tool holds the published cut-offs at nine anchor ages and interpolates between them, instead of the full LMS tables the WHO derives them from. That is accurate enough to place a child in a band and not accurate enough to argue about a single point.

What about children over five?

They are covered by a different reference, the WHO Growth Reference 2007 for ages 5 to 19. It is a separate set of tables and it is not built into this tool.

Is anything sent anywhere?

No. The arithmetic runs on your own device and the page makes no network request to do it, which is also why it works with no connection at all. What you typed is in the address bar so a refresh does not lose it.

Tips

Measure at the same time of day where you can — a full nappy is a genuine fraction of a small baby.
Below two years the WHO tables expect a lying-down length; from two, a standing height. They are about 0.7 cm apart.
Run it again after the next appointment. Two points make a direction; one makes nothing.
The address bar carries what you entered, so you can send the result to the other parent.

By Ahsan Mahmood · updated 2026-07-30

Open Child growth percentile calculator on LifeWell