Baby Weight Percentile Calculator

Reviewed by the CalculatorHub team, edited by James Graham. Method from WHO Child Growth Standards. Last verified 2026-06-23.

The Baby Weight Percentile Calculator computes baby weight percentile from the relation z = ((weight / M) raised to L minus 1) / (L x S); percentile = standard normal CDF of z x 100. It takes 4 inputs (baby weight in kg, lms reference l value for age and sex, lms reference m median weight for age and sex in kg, lms reference s coefficient of variation for age and sex) and returns the baby weight percentile. Because this is a pure mathematical or physical formula rather than a jurisdiction-specific rule, the result never changes over time: the same inputs always produce the same answer, so you can rely on it whether you are checking homework, sizing a design, or sanity-checking another tool. Enter your values in the fields below and the result updates instantly; you can also share a permalink that pre-fills the exact calculation, which is useful for teaching, reports, or collaboration. For example, with baby weight = 11 kg, lms reference l value for age and sex = 1, lms reference m median weight for age and sex = 10 kg, lms reference s coefficient of variation for age and sex = 0.1, the baby weight percentile works out to 84.134474, and the worked example further down the page shows every step so you can follow the arithmetic and reproduce it by hand. The method is the standard form documented by WHO Child Growth Standards, and the figure above each result carries the date it was last verified. This tool is general information and is not a substitute for professional engineering, medical, financial, or scientific advice; always check critical results against the primary source and your own judgement.