BMI Calculator

Enter your height and weight to calculate your BMI and body mass index classification.

Your Body Mass Index (BMI):

 
Scale showing range of BMI values and their categories. The canvas drawing shows this image with a marker showing where your BMI is on the range of BMI classifications.

BMI Classifications for Your Height[1]

Weight ranges for each classification based on your height.
BMI ClassificationWeight Range
underweight (< 18.5)
normal weight (18.5 - 24.9)
overweight (25.0 - 29.9)
class I obesity (30.0 - 34.9)
class II obesity (35.0 - 39.9)
class III obesity (≥ 40.0)


How to Calculate BMI

Body mass index, or BMI, is one of the most widely used metrics to measure health status. It is quick and easy to calculate to estimate one’s weight status based on their height.

BMI Formula

To calculate your body mass index, you only need to know your current height and weight. The formula for BMI is:

BMI = weight [kg]height² [m²]

Imperial Units

BMI = weight [lb]height² [in²] × 703

Or simply use the calculator above and it will do the work for you!

graphic showing the BMI formula, where BMI is equal to weight divided by height squared

Body Mass Index Categories

Once you calculate your BMI, you can then see where this falls on a body mass index chart such as the one below.

Studies have found that BMI is correlated with body fat and disease risk; therefore, BMI ranges are broken down into categories to estimate your nutritional status.[2]

These categories are: underweight, normal weight, overweight, and obese.[3] Obesity can also be broken down into class 1, class 2, and class 3 (or severe) obesity.

These ranges for BMI are based on the fact that excess body fat and obesity increases the risk of chronic diseases and premature death.

For example, being overweight or obese significantly increase the risk of heart disease, hypertension, and diabetes in both men and women. These diseases all subsequently increase morbidity and premature death.

BMI Chart

Body mass index weight categories defined by the CDC
Weight Category BMI
Underweight <18.5
Healthy Weight 18.5 – 24.9
Overweight 25 – 29.9
Class 1 Obesity 30 – <35
Class 2 Obesity 35 – <40
Class 3 Obesity >40

Is BMI Accurate?

While the BMI formula is a quick way to estimate health status and disease risk, it is not without fault. Since it only takes height and weight into consideration, it is not the perfect model for all individuals.

In addition, it does not directly measure body fat. As with all health calculations, it is an estimate of weight and body fat.[4]

For instance, bodybuilders and athletes may have a higher body weight. However, this is due to increased lean muscle mass and not fat mass (or adiposity).

Calculating their BMI would give a false impression that they are overweight or obese. Therefore, you have to take into account individual circumstances when using body mass index calculations.

The BMI tends to be a better predictor of body fat in individuals with higher levels of BMI. For instance, a person with a BMI above 35 or 40 is more likely obese. These extremely high numbers are less likely due to increased lean muscle mass.

How to Calculate BMI for Kids

BMI can also be used for young children and adolescents. While the same formula is used, the value is interpreted differently than adult BMIs.

For adults, BMI categories are the same regardless of age or gender. However, in young children and teenagers, BMI is age and sex-specific.

This is because body fat norms change with age and also differs between young boys and girls based on hormonal fluctuation.

As an example, a 7-year-old boy with a BMI of 20 would fall into the greater than 95th percentile and would be considered obese.

However, a 15-year-old boy with a BMI of 20 would fall between the 25th and 50th percentile and would be considered to be a healthy weight. These BMI charts can be accessed through the CDC website (boys[5] and girls[6]).

Body mass index for-age growth charts from the CDC take into account these differences and show BMI as a percentile ranking rather than falling into underweight, normal weight, or obese categories. These percentiles are determined using data collected from surveys of children from the U.S. population from 1963-65 to 1988-94.[7]

Categories for Children Ages 2-19

Body mass index weight categories for children ages 2-19 defined by the CDC
Weight Category Charting Percentile
Underweight <5th percentile
Healthy Weight 5th to <85th percentile
Overweight 85th to <95th percentile
Obese >95th percentile

BMI charting in kids is a useful way to diagnose health issues early on. In fact, one study from the Journal of Pediatrics found that pediatricians that utilized BMI charting had a greater recognition of weight problems in children compared to using height and weight charting alone.[8]

BMI in Men and Women

The BMI formula is the same for both adult men and women. However, men and women with the same body mass index can still have differing levels of body fat. In general, women tend to have more body fat than men due to differing hormone levels and physiology.

The BMI can also be used to help calculate an “ideal” body weight (IBW) for both men and women. In the past, separate equations for men and women have been used to determine IBW based on height. A commonly used equation for IBW is:

IBW Men [lbs] = 106 + 6 × (height [inches] – 60)
IBW Women [lbs] = 100 + 5 × (height [inches] – 60)

So, in this case, the ideal body weight for a 5′ 5″ woman would be 125 pounds, while the ideal body weight for a 5′ 5″ male would be 136 pounds.

However, a 2016 study found that using a target BMI in the IBW equation gives a more accurate representation of ideal body weight. This also replaces using two separate equations for men and women by adopting one universal equation.[9]

IBW [lbs] = 5 × BMI + ((BMI ÷ 5) × (height [inches] – 60))

This equation allows you to target a BMI and convert this to an ideal weight in pounds. Studies have found that a BMI around 22 confers the lowest morbidity in both men and women.[10] So using this formula, a 5′ 5″ woman targeting a healthy BMI of 22 would have an ideal body weight of 132 pounds.

Only One Aspect of Overall Health

As with all anthropometric calculations, BMI is only an estimate of body fat and health status. This calculation should not be used on its own to determine overall fitness or disease risk.

Age, sex, physical activity, lean muscle mass, waist circumference, and overall body composition can be used together with BMI to help form a complete picture of your health and fitness.

References

  1. World Health Organization, Body mass index - BMI, https://www.euro.who.int/en/health-topics/disease-prevention/nutrition/a-healthy-lifestyle/body-mass-index-bmi
  2. Garrow, J. S., & Webster, J., Quetelet's index (W/H2) as a measure of fatness, International journal of obesity, 1985, 9(2), 147-153. https://europepmc.org/article/med/4030199
  3. Centers for Disease Control and Prevention, About Adult BMI, https://www.cdc.gov/healthyweight/assessing/bmi/adult_bmi/index.html
  4. Prentice, A. M., & Jebb, S. A., Beyond body mass index, Obesity reviews, 2001, 2(3), 141-147. https://onlinelibrary.wiley.com/doi/abs/10.1046/j.1467-789x.2001.00031.x
  5. Centers for Disease Control and Prevention, 2 to 20 years: Boys Body mass index-for-age percentiles, https://www.cdc.gov/growthcharts/data/set1clinical/cj41l023.pdf
  6. Centers for Disease Control and Prevention, 2 to 20 years: Girls Body mass index-for-age percentiles, https://www.cdc.gov/growthcharts/data/set1clinical/cj41l024.pdf
  7. Centers for Disease Control and Prevention, About Child and Teen BMI, https://www.cdc.gov/healthyweight/assessing/bmi/childrens_bmi/about_childrens_bmi.html
  8. Perrin, E. M., Flower, K. B., & Ammerman, A. S., Body mass index charts: useful yet underused, The Journal of pediatrics, 2004, 144(4), 455-460. https://www.sciencedirect.com/science/article/abs/pii/S0022347604000927
  9. Peterson, C. M., Thomas, D. M., Blackburn, G. L., & Heymsfield, S. B., Universal equation for estimating ideal body weight and body weight at any BMI, The American journal of clinical nutrition, 2016, 103(5), 1197-1203. https://academic.oup.com/ajcn/article/103/5/1197/4569587
  10. Tokunaga, K., Matsuzawa, Y., Kotani, K., Keno, Y., Kobatake, T., Fujioka, S., & Tarui, S., Ideal body weight estimated from the body mass index with the lowest morbidity, International journal of obesity, 1991, 15(1), 1-5. https://europepmc.org/article/med/2010254