Baby Height Percentile Calculator

Growth Is Compared, Not Judged in Isolation

A single length measurement tells you almost nothing on its own — the same 65 cm could be perfectly typical for one 5-month-old and notably short for another. What matters is where that measurement falls relative to other infants the same age and sex, which is exactly what the World Health Organization's Child Growth Standards were built to answer, using data collected from healthy, breastfed infants across multiple countries.

The Formula

The calculator interpolates a median length for the entered age in months from WHO growth chart anchor points, estimates the standard deviation as roughly 4.2% of that median (consistent with WHO length-for-age tables), and converts the resulting z-score into a percentile using the normal cumulative distribution function.

WHO Median Length Reference Points (0–24 months)

These are interpolated approximations of WHO Child Growth Standards anchor points, used here for illustration — not a substitute for a pediatrician's official growth chart plotting.

Why Percentiles, Not Raw Length

• Tracking growth trends — a consistent percentile over several checkups matters more than any single measurement.
• Flagging when to ask questions — a sudden percentile shift (crossing two or more percentile lines) is one of the signals pediatricians watch for, more so than the percentile number itself.
• Comparing across sexes correctly — boys and girls grow at measurably different rates in infancy, which is why separate reference tables exist for each.

How to Use This Calculator

1. Enter your baby's age in months (0–24).
2. Select Boy or Girl.
3. Enter your baby's height (length) and choose cm or inches.
4. Select Calculate to see the estimated percentile and z-score.

Related Calculations

Check estimated weight before birth with the Baby Weight Calculator, or track feeding math with the Recipe Nutritional Calculator.