Baby Growth Percentile

The World Health Organization Child Growth Standards describe how children grew in a large study of babies who were fed in ways the WHO considers healthy, including breastfeeding. They are a reference, not a scoreboard. This tool uses the published LMS tables from birth through 730 days, separately for boys and girls, for weight in kilograms, length in centimetres, and head circumference in centimetres. The tables are the same numbers distributed with the WHO anthro reference files.

LMS is three numbers at each age. M is the median. S is a spread. L is a power that lets the curve be a little lopsided, which real body measurements are. The z-score is ((measurement divided by M) to the power L, minus 1) divided by (L times S). If L is zero, the formula uses a logarithm instead. The percentile is the share of the standard population below that z-score, from the normal curve. A measurement sitting on the median has a z-score of about 0 and a percentile of about 50.

Length, not height, is the right word under age two because the standard was measured lying down. A standing height is a different procedure and is not what this page expects. Head circumference is the distance around the largest part of the head, the way a clinic tape is used. A hat size from a shop is not a substitute. Weight should be a dry diaper and no heavy clothes if you want a number close to a clinic scale.

A percentile of 15 does not mean the baby failed. It means about 15 percent of children in the standard were lighter, shorter, or had a smaller head at that exact age and sex. Clinicians look at the pattern across visits, the birth size, the parents, and whether the child is ill or not feeding well. One afternoon’s number is a single dot. Crossing several curves downward, or a head measurement that jumps, is a reason to book a visit, not a reason to panic at the kitchen table.

The page will not calculate past 24 months. After the second birthday the WHO standard for older children is a different reference, and many countries switch the conversation to their own charts. It also refuses ages in the future and measurements of zero. Pounds are converted with the exact factor 0.45359237 kilograms per pound. Inches use 2.54 centimetres. Rounding the conversion yourself before you type will not match the page, so type the number you actually measured and let the tool convert.

This is not a diagnosis of underweight, overweight, microcephaly, or failure to thrive. Those words belong in a clinic, next to an examination. If you want the week of pregnancy that came before the birth date, use the week-by-week counter. For day-to-day care questions, the feeding and sleep overview points at WHO feeding guidance and tells you where it stops. Read the WHO Child Growth Standards documentation if you need the full method, and show this result to your own pediatric clinician before you change how you feed.