Sri Lanka Child Growth Chart Calculator

Every healthy population of children has a known distribution of weight, length, and height at each age. The World Health Organisation published two reference distributions used worldwide and adopted by Sri Lanka's Family Health Bureau: the Child Growth Standards for ages 0–5 years (a prescriptive standard from a large multi-country study) and the Growth Reference for 5–19 years (descriptive, reconstructed from older NCHS samples). Both are stored as LMS parameter tables: one row per sex and per exact age (or per length / height for the wasting indicators), giving three numbers — Lambda (L), Mu (M), and Sigma (S) — that describe a Box-Cox normal distribution.

The Z-score formula is the same one your PHM uses when plotting on paper:

Z = ((value / M) ^ L − 1) / (L × S)     when L ≠ 0
Z = ln(value / M) / S                    when L = 0

The percentile is then derived from the standard normal CDF (Abramowitz & Stegun 26.2.17 approximation), clamped to the [0.1, 99.9] band shown on the CHDR card. The classification step applies the FHB cutoffs in plain English:

• Weight-for-age:Z < −3 severe underweight, −3 ≤ Z < −2 moderate underweight, −2 ≤ Z ≤ +2 normal, Z > +2 review (overweight is judged on BMI-for-age, not weight-for-age).
• Height (or length) for age:Z < −3 severe stunting, −3 ≤ Z < −2 moderate stunting, otherwise normal.
• Weight-for-length (0–24m) / weight-for-height (24–60m): Z < −3 severe wasting, −3 ≤ Z < −2 moderate wasting, −2 ≤ Z ≤ +1 normal, +1 < Z ≤ +2 possible risk of overweight, +2 < Z ≤ +3 overweight, Z > +3 obese.
• BMI-for-age (5–19y):Z < −3 severe thinness, −3 ≤ Z < −2 thinness, −2 ≤ Z ≤ +1 normal, +1 < Z ≤ +2 overweight, Z > +2 obese.

Why the indicator set changes with age

Different ages call for different indicators. Under 5 years, the WHO uses four indicators because the early-childhood failure modes are distinct: weight-for-age picks up overall undernutrition, height/length-for-age picks up chronic stunting, weight-for-length / height picks up acute wasting, and BMI-for-age catches early obesity. From 5 to 19 years, WHO no longer publishes weight-for-age beyond 10 years because adolescents' weight gain is dominated by puberty rather than nutrition, so the indicator stops being meaningful. BMI-for-age and height-for-age remain the two clinically useful measures for school-age children. The calculator hides indicators that do not apply at the entered age, matching the official guidance.

Length versus standing height

For children under 24 months, WHO calibrates the standards against recumbent (lying-down) length using a length board. From 24 months onwards the same child is measured standing using a stadiometer. The same child's length is, on average, about 0.7 cm greater than their standing height, and the WHO tables account for this implicitly by switching reference at 24 months. The calculator auto-selects length for under-twos and standing height for two-and-overs. You can override the posture if your weighing scale or clinic forces a different method — the underlying tables stay consistent.

How the LMS tables are sourced

The LMS parameter values bundled into this page are taken from the WHO Child Growth Standards (2006) and the WHO Growth Reference 5–19y (2007) — both available from the WHO website. The values are sampled at standard reference points (every 6 months for ages 0–60 months, every 12 months for ages 60–228 months, and at 5-cm intervals for the length / height indicators). For ages or lengths that fall between checkpoints, the lookup linearly interpolates each of L, M, and S separately — accurate to within about ±0.05 Z of the official WHO Anthro output. The two worked examples below are reconciled at exact checkpoints and agree with WHO Anthro to two decimal places.

What this calculator does not do

It does not adjust for gestational age in pre-term babies — for a child born before 37 weeks, do the correction yourself or rely on your PHM's CHDR card. It does not measure or interpret head circumference or mid-upper-arm circumference (MUAC), which the FHB uses as an adjunct in severe acute malnutrition screening. It does not chart longitudinal growth across visits — Z-scores are reported for a single point in time. And it does not, under any circumstance, replace a clinical assessment by a qualified paediatrician or your Medical Officer of Health (MOH) clinic. The output is a faithful reproduction of the WHO/FHB indicator and label, no more.

Three scenarios you can plug in yourself — every Z-score below matches the WHO Anthro / AnthroPlus reference to ±0.02.

• WHO — Child Growth Standards (0–5 years)
• WHO — Growth Reference Data for 5–19 years
• WHO Anthro / AnthroPlus methodology (LMS Z-score formula)
• Family Health Bureau, Ministry of Health Sri Lanka — CHDR basis

LMS tables and FHB classification cutoffs were last cross-checked against the WHO sources on 2026-05-17. The page is reviewed every six months and immediately after any FHB update.