Bodies come in many different shapes and sizes. And with this comes many different weights and heights among people of all ages.
As an adult, it can be easy to compare your body to those of other people, but this can be harmful especially since there are a lot of ways to look and be healthy.
But when it comes to children, it’s sometimes necessary to see how their weight and height stack up to their peers. This can help parents and pediatricians know if kids are growing properly. And this is where BMI percentile comes in.
Read on to learn more about BMI, including how it was invented, plus how to calculate BMI percentile and what your results may mean.
What is body mass index (BMI)?
BMI (body mass index) is a calculation that uses a person’s height and weight to estimate body fat and general health risks.1 BMI is categorized into 4 basic categories: underweight, normal weight, overweight, and obese.
It would make sense for BMI to have been invented by a healthcare provider or health scientist. However, the truth is quite different.
BMI was created by a statistician named Lambert Adolphe Jacque Quetelet. He hoped to use his BMI equation to find the average size of men and women. Interestingly, though, he never meant for BMI to be used in the medical field at all.
In the 1970s, BMI became widely used in population-based studies and, eventually, in healthcare providers’ offices.2
It’s important to point out that even the original creators of BMI never thought of it as a good representation of a person’s body fat or health. Although BMI may be a good starting point for conversations about your health, it’s seen by many as insufficient as a sole way of classifying someone as underweight, obese, or even healthy.
This is because BMI doesn’t allow for variations in body shape, body size, and muscle mass. This often leads to the strongest athletes in the world being classified as obese, an indicator that is obviously wrong.
Despite any issues with BMI, it’s still widely used in healthcare settings. However, BMI itself is mostly used for adults, while BMI percentile is used for children and teens.
How to calculate BMI percentile
Because kids are constantly growing, it’s important to keep up with their growth to make sure they’re doing so properly. This is where BMI percentile comes in.
If you’re a parent, then you know that you’re given growth charts every time you visit the pediatrician, and one of these is for BMI percentile. This growth chart may say something like “BMI-for-age percentiles: boys, 2-20 years”. BMI percentile is meant to compare a child’s BMI to other children in the US of the same gender and age.3
Manual calculation
You can calculate BMI using the formulas below:
- Metric – weight (kg) / [height (m)]2
- Imperial – weight (lb) / [height (in)]2 x 703
Once you have this number, you can then plot it on a BMI percentile chart.
BMI percentile calculator
Alternatively, you can simply use the widget below to calculate BMI percentile.
Once you have the BMI percentile, you’ll be able to use the following classifications:
- Underweight: below the 5th percentile
- Healthy weight: between the 5th and 85th percentile
- Overweight: between the 85th and 95th percentile
- Obese: greater than or equal to the 95th percentile4
What can BMI percentile tell you about a child’s health?
BMI percentile is a simple way to assess body fat, which may be used to assess the potential risk of chronic health problems. However, it’s important to note that BMI has flaws and should not be the only tool used to assess health or body fat. Other measures like waist-to-height ratio and waist circumference are thought to be better indicators of health outcomes.
Children with a BMI percentage over the 85th percentile should be evaluated by a health professional. However, having a high BMI doesn’t automatically make a child unhealthy or mean that they will develop a chronic issue. Recall that many athletes have high BMIs.
A child or teen can take simple steps to improve their BMI. This may be as simple as eating less (or more if they are underweight), eating a healthier diet, or getting more exercise.
About Brittany Lubeck
Brittany Lubeck is a registered dietitian and nutrition writer. She has a Bachelor of Science in Dietetics, a Master of Science in Clinical Nutrition, and began her career as a clinical dietitian. Brittany has always enjoyed research and loves that she can help people learn more about nutrition through her writing.
Sources:
1. Weir, C.B., & A. Jan. BMI Classification Percentile And Cut Off Points (Treasure Island, FL: StatPearls Publishing, 2022).
2. Nuttall, F. Q. “Body Mass Index.” Nutrition Today 3, no. 50 (2015): 117-128.
3. “About Child & Teen BMI.” U.S. Department of Health & Human Services. CDC.gov.
4. Zierle-Ghosh, A., & A. Jan. Physiology, Body Mass Index. (Treasure Island, FL: StatPearls Publishing, 2022).
