The rules behind the numbers
How We Build These Tables Methodology & sources
Most "average for age" numbers online come with no source. Ours come with this page. Every value in the benchmark section is computed from a named public dataset, by a stated method, with the reference population labeled — and where no legally-clear youth data exists for a test, we say so on the page instead of inventing a number.
Datasets in use today
- CDC Growth Charts (2000) — National Center for Health Statistics. Public domain (a work of the U.S. government). Coverage: stature, weight, and BMI for ages 2–20, both sexes, published as LMS parameters. This powers every growth and height page. Use of these data does not imply endorsement by CDC, NCHS, HHS, or the U.S. government.
Planned next: percentiles for youth fitness measures computed from the CDC National Youth Fitness Survey (NNYFS, 2012) public-use files with the survey's own examination weights, validated against CDC's published summaries before anything ships. Until that work is finished and validated, no fitness-test number appears anywhere on this site.
The method
The CDC publishes an LMS triplet — skewness (L), median (M), and coefficient of variation (S) — for each age (in months) and sex. A percentile value is computed as X = M·(1 + L·S·z)1/L for the standard-normal z of that percentile, and a measurement is converted to a percentile through the same formula inverted — exactly the computation the printed growth charts are built from. We interpolate linearly between the published age points, never beyond the table's ends (ages 2–20), and displayed percentiles are capped to the 1st–99th band: outside it, pages say "outside the reference range" rather than showing a more extreme-sounding number.
Calculators run this math in your browser from the public parameter table. Nothing you enter is transmitted, stored, or attached to analytics.
Publishing rules we hold ourselves to
- No invented numbers. No value appears unless it is computed from a legally-clear, named source. "Typical ranges" without a dataset behind them don't ship.
- Licensed tables stay unpublished. Several well-known youth norm tables are licensed or restricted; we do not reproduce them, excerpt them, or "adapt" them. Where that leaves a gap, the page says so honestly.
- Population labels on every table. Who was measured, when, and where — because a reference population is context, not a target.
- Reference, not judgment. No result is framed as a health verdict, a grade, or a prediction. Health questions go to your pediatrician; training decisions go to your athlete's coach.
- Dated pages. Every page shows when it was published and last reviewed, and this page records changes below.
Change log
- August 26, 2026 — Section launched: height percentile calculator, height reference tables (ages 12–14), measurement protocol, and percentile guide, all computed from the CDC Growth Charts (2000). Page last reviewed: August 26, 2026.
Source: CDC Growth Charts (2000), National Center for Health Statistics — cdc.gov/growthcharts. Reference population: the U.S. reference population underlying the CDC Growth Charts (2000).
One number tells you where they are today.
The part that actually matters is the same measurement, repeated over a season — the record of measured change over time. That's what My Athlete keeps, across 18 sports, alongside every assessment your athlete does.