How far apart should two measurements be?

At least three months, and six to twelve is better. Below 90 days this page will not return a rate at all, because the error in two measurements is larger than the growth between them.

Is this growth rate normal?

That question needs WHO’s velocity tables, which are not among the standards behind these figures, so no reference exists to place a rate against. Take a rate that worries you to a paediatrician, with the measurements and dates it came from.

Why does a short gap give such a large number?

Because annualising multiplies the error too. Half a centimetre measured two weeks apart annualises to about 13 cm a year — a figure made almost entirely of measurement noise. That is the reason for the 90-day floor.

Calculators

Growth velocity calculator

How fast a child grew between two measurements, in cm per year. Two dates and two heights is all it needs — and if they are too close together, this page says so rather than returning a number.

Fill in the fields to see the position

How to read this number

A rate is only as good as the gap it is measured over. Under about three months, the difference between two measurements is mostly shoes, posture and time of day rather than growth: a six-year-old grows about 0.4 cm in a month, less than a single measurement’s error. Multiplying that up gives a confident-looking figure built almost entirely from noise, which is why intervals shorter than 90 days get no number here.

What the rate is useful for is the same thing percentiles are useful for — whether it holds. One slow-looking interval means little; a rate that stays low across a year is what a clinician wants to see, with the measurements that produced it.

No percentile is given for the rate itself. WHO publishes velocity tables, but they are not among the standards behind these figures, and without them no rate could honestly be called normal or otherwise.

The standard behind it

This calculator uses WHO Child Growth Standards (2006) · WHO Growth Reference (2007)’s LMS parameters. Ages 0–5 use the 2006 Child Growth Standards and 5–19 the 2007 growth reference; the two join at five.

The source tables are taken straight from who.int, data version 2026-08-25. Ages beyond what a standard covers are never extrapolated — the page says there is nothing there.

Common questions

How far apart should two measurements be?: At least three months, and six to twelve is better. Below 90 days this page will not return a rate at all, because the error in two measurements is larger than the growth between them.
Is this growth rate normal?: That question needs WHO’s velocity tables, which are not among the standards behind these figures, so no reference exists to place a rate against. Take a rate that worries you to a paediatrician, with the measurements and dates it came from.
Why does a short gap give such a large number?: Because annualising multiplies the error too. Half a centimetre measured two weeks apart annualises to about 13 cm a year — a figure made almost entirely of measurement noise. That is the reason for the 90-day floor.