What data does this calculator use?

For 0-24 months it uses the WHO Child Growth Standards (2006), and for ages 2-20 it uses the CDC 2000 Growth Charts - the same dual standard the CDC and the American Academy of Pediatrics recommend for the United States (WHO charts under age 2, CDC charts from age 2).

Baby & Child Growth Percentile Calculator

Q: Is a low or high percentile a problem?

A single measurement is not a diagnosis. What matters most is the trend of the growth curve over time. If your child is below the 3rd or above the 97th percentile, or has crossed two or more percentile lines, bring it up with your pediatrician. This calculator is for reference only.

How it works

Pick your child's sex and age, then enter height and/or weight — you can use US units (in, lb) or metric (cm, kg) with the toggle at the top. The calculator instantly shows the percentile: your child's position among 100 children of the same age and sex. You'll also see a normal-range assessment (3rd–97th percentile) and the reference values for that age (3rd, 50th, and 97th percentiles). Entering just one of height or weight is fine. For babies up to 24 months, height means length measured lying down; from age 2, it means standing height.

Data sources — WHO (0–24 months) + CDC (2–20 years)

This calculator follows the dual standard recommended for the United States by the CDC and the American Academy of Pediatrics: the WHO Child Growth Standards for children under 2, and the CDC 2000 Growth Charts from age 2 up (see cdc.gov/growthcharts/who-charts.htm). It embeds the officially published LMS parameters from both sources:

0–24 months: WHO Child Growth Standards (2006) — length-for-age and weight-for-age LMS tables (who.int/tools/child-growth-standards/standards). Verified against published medians, e.g. boys at 12 months: length 75.7 cm, weight 9.6 kg.
2–20 years: CDC Growth Charts LMS data files — statage.csv (stature-for-age) and wtage.csv (weight-for-age) from cdc.gov/growthcharts/data/zscore/ (listed at cdc.gov/growthcharts/cdc-data-files.htm). The embedded values were checked against the published 3rd/50th/97th percentile columns of those files (maximum deviation under 0.01 cm/kg).

Your measurement is converted to a z-score with the LMS method — z = ((X/M)^L − 1) ÷ (L·S) — and then to a percentile through the normal distribution, the same math behind pediatric growth-chart tools. Ages are handled as completed months; for ages 2–20 the calculator uses the CDC LMS values at the age-interval midpoint, matching how the CDC data files are constructed. US-unit inputs are converted exactly (1 in = 2.54 cm, 1 lb = 0.45359237 kg).

Examples

A 12-month-old boy measuring 29.8 in (75.7 cm) is right at the WHO median — about the 50th percentile, meaning longer than roughly half of boys his age. A 10-year-old boy at 54.6 in (138.8 cm) sits at the CDC median for his age — again about the 50th percentile. If that same 10-year-old were 51 in (129.5 cm), he'd be around the 7th percentile: within the normal range, but on the shorter side, and worth watching over time. Remember that the trend of the curve matters more than any single reading — crossing two or more percentile lines up or down is a better reason to check in with your pediatrician than any one number.

FAQ

What is a growth percentile?

It's your child's position among 100 children of the same age and sex, lined up smallest to largest. A height in the 60th percentile means taller than about 60 of them; the 50th percentile is exactly the median. Between the 3rd and 97th percentile is generally considered the normal range.

Why two different charts?

The WHO standards (0–24 months) describe how healthy, predominantly breastfed infants should grow under optimal conditions, while the CDC charts (2–20 years) describe how US children actually grew in national survey data. The CDC recommends WHO charts under age 2 and CDC charts from age 2 — this calculator switches automatically with the age group you pick. Note that lengths up to 24 months are measured lying down, which reads about 0.8 cm (0.3 in) longer than standing height.

Is a low or high percentile a problem?

Not by itself. Consistently tracking along the 10th percentile can be perfectly healthy. Talk to your pediatrician if your child is below the 3rd or above the 97th percentile, or if the percentile has changed sharply between checkups. Preterm babies should be assessed using corrected age, which this calculator does not apply — follow your pediatrician's assessment.

Is anything I type stored?

No. Every calculation runs entirely in your browser — nothing you enter is sent to or stored on a server.

Medical disclaimer: This calculator is for informational purposes only and is not medical advice, diagnosis, or treatment. Growth assessment depends on accurate measurement technique and clinical context — always rely on your pediatrician or family doctor for any decisions about your child's growth and health.