以下详细说明暂以英文提供。
Why children are not scored like adults
Body fat changes naturally as children grow, and it changes differently for boys and girls, so a single fixed healthy range would mislabel most of them. Pediatricians therefore plot BMI on BMI-for-age growth charts and read off a percentile: the 75th percentile means a child carries more relative mass than 75 of 100 peers of the same age and sex. Roughly, the 5th to 85th percentiles are considered healthy, 85th to 95th overweight, and at or above the 95th obese. The category this calculator shows applies adult cut-offs as a blunt approximation and is labeled accordingly.
Getting a usable number
Measure height without shoes against a wall and weight in light clothing, and record both to the nearest sensible unit. Track the trend over time rather than reacting to one reading: a child who jumps percentiles on the chart in either direction is the pattern pediatricians act on. Height and weight happen in spurts, so an unusually high or low single BMI often simply marks the week of a growth spurt. Any concerns belong with your child’s doctor, who can plot exact percentiles and interpret them alongside family history.
中国本地参考
日常计算时值得知道的中国本地规则：
- 计量的单位习惯: 住房面积用平方米，土地常用亩（1 亩 ≈ 666.7 平方米）；里程用公里，油耗用 L/100km。
- 日期与数字格式: 日期写作 2026年10月13日（年-月-日）；大数习惯用万、亿（1 万 = 10,000，1 亿 = 100,000,000）。
- 法定节假日: 全年法定节假日 11 天，春节与国庆为长假；调休安排每年由国务院办公厅发布。
- 速度与限速: 高速公路最高限速 120 km/h，城市快速路多为 80 km/h，均以公里每小时计。
- 鞋服尺码: 鞋码用中国码（毫米制），服装常用 155/80A 这类身高围度组合，与欧美码不同。
数据核对：2026 年 10 月
常见问题
Is my child’s BMI interpreted the same as an adult’s?
No. Children are assessed by percentile against CDC growth charts for their age and sex, so the adult labels shown here are only a rough orientation. A BMI of 17 might sit in the healthy range for a 10-year-old but underweight territory for a 17-year-old.
Where can I get the exact percentile?
Your pediatrician can plot the measurement on the official CDC BMI-for-age charts, and the CDC publishes downloadable chart PDFs. Bring the BMI number from this page along with age, sex, height, and weight to the appointment.
How is BMI calculated here?
The same formula as adults: weight in kilograms divided by height in meters squared. Pounds and inches are converted first (1 lb = 0.4536 kg, 1 in = 2.54 cm). Example: 35 kg at 140 cm gives 35 ÷ 1.96 = about 17.9.