How it works
This calculator uses the WHO 2006 Child Growth Standards LMS tables (L = Box-Cox power, M = median, S = coefficient of variation) to compute a Z-score, then converts it to a percentile via the cumulative normal distribution. The standards come from a six-country, multi-ethnic study of breastfed infants and reflect normal growth globally, for ages 0–5 (height, weight, head circumference).
How to read the results
WHO percentiles are a statistical reference, not a verdict. A single measurement should never stand on its own — keep these in mind.
- Trend over time matters more than a single percentile. A drop of two or more percentile groups (e.g. 50→15) warrants a pediatric visit.
- Ages 0–5 only. Above age 5, country-specific standards (CDC, etc.) apply — this calculator does not yet cover them.
- WHO vs CDC vs national standards. Country-specific charts (Korean, Japanese, CDC) may fit your child better. This calculator uses the global WHO standard only.
- Measurement error. Length (lying, 0–24 months) and height (standing, 2–5 years) use different techniques — keep the method consistent for tracking.
Frequently asked questions
Is a low percentile a problem?
A single percentile can't answer that. Anywhere between the 5th and 95th percentile is within the normal range, and the trend matters far more than a single reading. Talk to a pediatrician if your child drops two or more percentile bands or stays below the 3rd percentile.
Should I use WHO, CDC, or a national standard?
The CDC and most pediatric societies recommend the WHO standard for ages 0–2, then switch to a national chart afterward. This calculator uses WHO for the full 0–5 range.
My readings jump around — which one is right?
Home measurements often vary by ±1–2 cm and ±0.3 kg depending on posture, clothing, and time of day. Measure at the same time of day with the same method and watch the trend. Well-baby visits are the most consistent reference.