Baby growth percentiles from the official WHO standards, birth to 24 months: weight-for-age, length-for-age and head circumference in one calculation, with z-scores and medians.
| Input | Result |
|---|---|
| 12-month-old boy, 9.6 kg, 75.7 cm, head 46.1 cm | weight 48th · length 49th · head 51st percentile |
| 12-month-old boy, 10.8 kg | weight about the 85th percentile |
| 6-month-old girl, 7.3 kg | weight about the 50th percentile |
| Newborn boy, 3.3 kg, 49.9 cm, head 34.5 cm | 46th / 50th / 51st percentile |
A growth percentile compares your child with a reference population of the same age and sex — not with "normal". The 50th percentile is the median, not a target. A healthy child can sit steadily at the 10th percentile for years, and that is a different situation from a child who drops from the 60th to the 10th in six months.
This is why pediatric practice looks at the curve, not the number. A single measurement tells you where a child is; two or three measurements over time tell you how they are growing, which is the thing that actually carries information. Very few children track a constant percentile — most move up or down one band between visits and that is normal.
The reference values are the WHO Child Growth Standards, published by the World Health Organization from its Multicentre Growth Reference Study, which followed healthy, breastfed infants in six countries. WHO releases the standards as LMS parameters — the official machine-readable form of the growth curves:
M is the median (50th percentile), S the coefficient of variation and L the skewness power. Head circumference uses L = 1, so the formula simplifies to z = (X/M − 1) / S. Age is interpolated linearly between WHO's published whole-month rows.
The data embedded in this page are the WHO files themselves (the same tables pediatric clinics plot against), not estimates or re-digitized curves.
The M column of the WHO LMS file is the published 50th percentile, so these are the reference values themselves, read straight from the WHO tables.
| Age | Boys | Girls |
|---|---|---|
| 0 months | 3.35 kg | 3.23 kg |
| 3 months | 6.38 kg | 5.85 kg |
| 6 months | 7.93 kg | 7.30 kg |
| 9 months | 8.90 kg | 8.23 kg |
| 12 months | 9.65 kg | 8.95 kg |
| 15 months | 10.31 kg | 9.60 kg |
| 18 months | 10.94 kg | 10.23 kg |
| 21 months | 11.55 kg | 10.85 kg |
| 24 months | 12.15 kg | 11.48 kg |
| Age | Correct reference | Where on this site |
|---|---|---|
| 0–2 years | WHO growth standards | This page. The CDC and the American Academy of Pediatrics both recommend WHO charts for under-2s. |
| 2–20 years | CDC 2000 growth charts | Child weight, child height and child BMI calculators. |
Switching charts at age 2 produces a small visible step in the curve, because the two references were built from different populations. Keep a child's series on one chart per age band.
For children under 2, both the CDC and the American Academy of Pediatrics recommend the WHO growth standards, which this page uses. From age 2 to 20 the CDC 2000 charts are the US reference — this site has separate child weight, height and BMI calculators for that range.
The WHO charts plot the 3rd to the 97th percentile, and anywhere inside that band can be entirely normal. A baby who tracks steadily near the 10th percentile is usually just small, not behind; a baby who drops across two or more percentile lines is the pattern pediatricians act on. One reading means little, the curve means a lot.
Lay the baby flat on a firm surface, head touching a wall or board, legs gently straightened, and mark where the heels land. Home measurements typically err by half to a full centimetre, so treat small percentile moves as noise. Clinic length boards are the accurate version.
Weighing too often adds anxiety without adding information — home scales vary by 100 grams or more and babies vary by feed. Monthly is plenty for routine tracking outside the pediatric visit schedule, which already measures at each well-child visit.
They were built differently. The WHO standards describe how healthy breastfed infants in six countries actually grew (a prescriptive standard), while the CDC 2000 charts describe how a mixed US sample grew between 1963 and 1994 (a descriptive reference). A baby can legitimately sit at different percentiles on the two charts.