Measure Height 
How it works
The CDC 2000 growth charts are built from US national survey measurements of children taken between 1963 and 1994. For every half month of age from 2 to 20 the CDC publishes three numbers, L, M and S, that describe the full height and weight distribution at that age. M is the median, S is the spread and L corrects for skew, which matters a lot for weight.
The calculator turns the child's measurement into a z-score with the LMS formula, then into a percentile. It uses the age in completed months, as the CDC tables do. Nothing is read off a picture of a chart, so a child halfway between the 50th and 75th lines gets a real number such as 63rd, not "between 50 and 75".
Under 2? Use the baby height percentile calculator, which runs on the WHO standards the CDC recommends for that age.
Worked examples
| Child | Height | Pct | Weight | Pct |
|---|---|---|---|---|
| Boy, 8 y | 127 cm (4'2") | 42nd | 25.4 kg (56 lb) | 46th |
| Girl, 12 y | 152 cm (5'0") | 53rd | 42 kg (92.6 lb) | 51st |
| Boy, 15 y | 172.7 cm (5'8") | 63rd | 59 kg (130 lb) | 59th |
| Girl, 5 y | 105 cm (3'5.5") | 27th | 17 kg (37.5 lb) | 33rd |
| Boy, 3 y | 91 cm (3'0") | 13th | 13 kg (28.7 lb) | 17th |
The 3-year-old boy is the interesting one. At the 13th percentile for height and 17th for weight he is a small, proportionate child. Height and weight sitting close together is reassuring; a wide gap between them is what to ask about.
Reading the result
- One reading says little. The value is in the line over time. Save the share link after each measurement and you have a history.
- Steady is healthy. A child who has been on the 10th percentile since age 3 is growing normally for them.
- Crossing lines is the signal. Dropping from the 50th to below the 25th in a year, without an obvious reason such as the start of puberty, is worth a visit.
- Teen percentiles bounce. Between 10 and 15, early and late maturers move up and down the chart while they are on different schedules.
Measurement error moves percentiles more than people expect. At age 8, one centimetre of height is worth about 7 percentile points near the middle of the chart. Shoes, hair and a slouch add up to that easily. Once you have a good reading, the height predictor projects it to adult height.
Questions
What does the 50th percentile mean?
Half of children of the same age and sex in the CDC reference are shorter (or lighter) and half are taller. The 25th percentile means 25 out of 100 are below. It is a position, not a score, and the 50th is not a target.
What percentile is too low or too high?
Clinics usually look twice at a height below the 3rd or above the 97th percentile. More important than any single reading is the trend: a child who drops or climbs across two of the main lines (5th, 10th, 25th, 50th, 75th, 90th, 95th) between visits should be checked, whatever the starting point.
Is weight percentile the same as BMI percentile?
No. Weight-for-age ignores height, so a tall child will have a high weight percentile without being heavy for their size. The CDC uses BMI-for-age to judge weight status. If the weight percentile is far from the height percentile, ask your pediatrician for the BMI percentile.
Why does it start at age 2?
The CDC recommends its own charts from age 2 and the WHO growth standards before that. Children under 2 are also measured lying down, which reads slightly longer than standing height.
Are these the same charts my pediatrician uses?
In the US, yes: the CDC 2000 stature-for-age and weight-for-age charts for ages 2 to 20. The calculator uses the LMS values those charts are drawn from, so the percentile is exact rather than read off a printed line.
Source: CDC 2000 growth charts, stature-for-age and weight-for-age LMS data, ages 2 to 20 (Kuczmarski et al., Vital Health Stat 11(246), 2002). For screening and curiosity, not diagnosis.