BMI at age 11
Children and teens are compared with others of the same age and sex. BMI is read as a percentile. This page shows how that works at age 11.
How it works
BMI is weight in kilograms divided by height in meters squared. The page then looks up three CDC values for the age and sex: L, M and S. The z score is ((BMI divided by M) to the power L minus 1) divided by (L times S). The percentile comes from the z score. At age 11 the median BMI is 17.2 for males and 17.5 for females. This male example is 0.1 from its median.
Worked example
Take a boy aged 11 who is 4 ft 9 in tall and weighs 79 lb. In metric that is 144.78 cm and 35.834 kg. Square the height: 1.4478 × 1.4478 = 2.0961. Divide 35.834 by 2.0961 to get a BMI of 17.0956. The CDC table for males at age 11 gives L -2.5906, M 17.201 and S 0.12673. Divide the BMI by M: 17.0956 divided by 17.201 = 0.993872. Raise that to the power L to get 1.016052. Subtract 1 to get 0.016052. Divide by L × S: 0.016052 divided by (-2.5906 × 0.12673) = -0.049. A z score of -0.049 is the 48th percentile, which is in the healthy weight band.
At age 11, a boy and a girl each at the CDC median height and the weight that gives the median BMI. The form above is set to the boy.
- Male at median height and weight (4 ft 9 in, 79 lb)
- BMI 17.1, 48th percentile
- Female at median height and weight (4 ft 9 in, 81 lb)
- BMI 17.5, 51st percentile
Common questions
What is the median BMI at age 11?
On the CDC chart the median is 17.2 for males and 17.5 for females at age 11. The example BMI of 17.1 is 0.1 away from the male median of 17.2.
Does BMI show body fat in a child?
Only roughly. BMI uses height and weight. A muscular child can score high. A doctor looks at growth over time as well as the number. A BMI of 17.1 for this boy at age 11 says nothing about how much of the 79 lb is muscle.
Why does BMI change as a child grows?
BMI usually falls through early childhood and then rises through the teen years. That is normal growth, which is why the chart is built by age. The median BMI for males is 17.2 at age 11.
What should I do if my child is above the 85th percentile?
One reading is not a diagnosis. Raise it with your child's doctor, who can look at growth history and the whole picture. The 85th percentile BMI for males at age 11 is 20.2.
Which ages does this calculator cover?
It covers ages 2 to 20, the range of the CDC growth charts. For adults over 20 use the adult BMI calculator. This page reads the CDC male table at 132.5 months.