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 source — the CDC 2000 Growth Charts, and why not WHO
This calculator uses the CDC 2000 Growth Charts for the whole range, with the LMS parameters exactly as the CDC publishes them:
- 0–24 months: CDC infant charts — length-for-age (lenageinf.csv) and weight-for-age (wtageinf.csv) from cdc.gov/growthcharts/data/zscore/. The embedded values were checked against the published percentile columns of those files (maximum deviation 0.0012 cm/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).
- Source pages: CDC growth chart data files · CDC guidance on using WHO charts under age 2
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 30.0 in (76.1 cm) is right at the CDC 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.
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.
Frequently asked questions
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.
What data does this use, and why CDC rather than WHO under age 2?
The CDC 2000 Growth Charts across the whole range: the infant charts (length- and weight-for-age) for 0–24 months and the child charts (stature- and weight-for-age) for ages 2–20, using the LMS parameters exactly as the CDC publishes them. One honest caveat: for children under 2 the CDC and the American Academy of Pediatrics recommend the WHO growth standards, which describe how healthy, predominantly breastfed infants should grow. WHO publishes those tables under a licence that does not permit commercial use, and an ad-supported page is commercial use — so this calculator uses the CDC infant charts, the official US reference before 2010 and public-domain US government data. The two references can differ by a few percentile points under 24 months (WHO runs slightly lighter and shorter); if your pediatrician plots on WHO charts, expect small differences. From age 2 up there is no such gap. 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 — a single measurement is not a diagnosis, and consistently tracking along the 10th percentile can be perfectly healthy. What matters most is the trend of the curve over time. Talk to your pediatrician if your child is below the 3rd or above the 97th percentile, or has crossed two or more percentile lines between checkups. Preterm babies should be assessed using corrected age, which this calculator does not apply. This calculator is for reference only.
Is anything I type stored?
No. Every calculation runs entirely in your browser — nothing you enter is sent to or stored on a server.