Child Growth Percentiles (CDC & WHO)

How we calculate child growth percentiles

This tool uses the LMS method applied by the US Centers for Disease Control and Prevention (CDC) and the World Health Organization (WHO) to convert a measurement (weight, length/height, BMI, or head circumference) into a z-score and percentile. In short, the LMS tables provide three values for each age (or length/height): L (skewness), M (median), and S (coefficient of variation). The z-score is computed as ((X/M)L−1)/(L·S) (or ln(X/M)/S when L=0); the percentile comes from the standard normal CDF. CDC supplies LMS tables for ages 0–36 months and 2–20 years, and WHO provides international standards for 0–5 years. :contentReference[oaicite:1]{index=1}

• Standards: By default we use WHO for 0–5 years and CDC for 2–20 years. You can override this behavior with the “Standard” selector. :contentReference[oaicite:2]{index=2}
• Measurements supported: Weight-for-age, length/height-for-age, BMI-for-age, and head circumference-for-age (head circumference available on WHO 0–5y and CDC 0–36m tables). Weight-for-length/height is supported where the corresponding LMS tables are available. :contentReference[oaicite:3]{index=3}
• Unit handling: Enter values in kg/cm or lb/in; we convert internally before calculation.
• Gentle display: Percentiles are shown on a calm bar: below 5th and above 95th are highlighted only to encourage follow-up, not judgment.

Source files and formulas are from CDC and WHO publications and data pages linked above. Always interpret growth in clinical context.

How to take accurate child measurements (WHO-style)

Accurate measurements make percentiles meaningful. The tips below summarise WHO good-practice techniques for weight, length/height, and head circumference. Use calm, repeatable routines; if a reading looks surprising, take a second measurement and record the average.

Before you start

• Time of day: Measure at roughly the same time on follow-ups (e.g., morning), before a big meal if possible.
• Clothing: Minimal/light clothing for weight; remove hats, bulky jumpers, shoes, nappies if feasible.
• Equipment check: Digital scale on a firm, level floor; length board or stadiometer fixed and square; flexible, non-stretch tape for head circumference.
• Calm setup: Warm room, soft surface nearby for infants, and a helper for length in under-2s.

Weight (all ages)

• Zero/tare the scale. Stand (or place infant) centred, still, and looking ahead; wait for the reading to stabilise.
• Infants: Use an infant scale. If unavailable, weigh the caregiver alone, then caregiver holding infant; subtract the two.
• Record: To the nearest 0.01 kg (or 0.1 lb). Repeat once; if values differ by >0.1 kg, take a third and use the average of the two closest.

Recumbent length (<2 years)

• Two people if possible: One aligns the head; the other straightens the legs and slides the footpiece.
• Position: Child lies on a flat length board. Head touches the fixed headboard with eyes looking straight up (Frankfort plane), shoulders and bottom flat, legs gently straight, feet at 90°.
• Read & record: To the nearest 0.1 cm. Take a second measurement; if they differ by >0.5 cm, take a third and average the two closest.

Standing height (≈≥2 years)

• Stadiometer: Child stands barefoot, heels together, legs straight, shoulders relaxed, arms at sides.
• Head position: Eyes looking forward (Frankfort plane horizontal). Ensure heels, calves, buttocks, and upper back lightly touch the board if comfortable.
• Headpiece down: Bring it to the crown with gentle pressure. Read to 0.1 cm. Repeat; if >0.5 cm apart, measure a third time and average the nearest two.

Head circumference (0–5 years)

• Tape placement: Wrap a non-stretch tape above the eyebrows and ears, around the widest part of the back of the head (occipital prominence).
• Snug but not tight: Keep the tape level all the way round. Read to 0.1 cm. Repeat once and average.

Consistency & recording

• Note context: Recumbent vs standing, diaper on/off, clothing, time of day, and if the child was unsettled.
• Use the same equipment on follow-ups where possible; calibrate scales regularly.
• Enter values as measured: Our tool handles unit conversion and the small length↔height adjustment used in growth standards.

Example entries (for your calculator)

• Infant (9 months): Weight 9.70 kg (infant scale, light vest), Recumbent length 72.0 cm (two measurers), Head circumference 45.0 cm.
• Toddler (2 years 3 months): Weight 12.8 kg, Standing height 88.4 cm (stadiometer), Head circumference optional.
• Child (5 years): Weight 18.6 kg, Standing height 109.2 cm. Take two readings and use the closest pair.

These techniques reflect widely used WHO measurement practices for growth assessment. If a reading seems unexpected, re-measure, check technique, and consider trends over time rather than a single point.