Baby Weight Percentile Calculator (WHO, 0–24 Months)

How to use

1. Pick boy or girl and enter the age in completed months (0–24).
2. Choose lb (default) or kg and type the measured weight.
3. Press Get percentile to see the z-score and percentile.
4. Read the plain-English interpretation and share it with your pediatrician.

General information only — not medical, financial or legal advice. Figures cross-checked against public official sources (IRS / HMRC / NHS / WHO guidance); content last reviewed September 2026. For decisions that matter, confirm with a licensed professional in your country.

About this tool

This calculator places a baby weight on the official WHO Child Growth Standards weight-for-age curve for children from 0 to 24 completed months, using the published L, M, S values for boys and girls. The math is the standard one: a z-score of ((x/M)^L − 1)/(L×S) turns the measurement and age into a position on the curve, and the percentile comes from the normal distribution — the 60th percentile means roughly 60 of 100 babies of the same age and sex weigh less. Weights default to pounds with a kilogram toggle. Professional measurements beat bathroom scales, and a single point matters far less than the trend across visits, so take the result to your pediatrician rather than acting on it alone. It is an educational estimate — not medical advice.

FAQ

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