Body Mass Index (BMI) Calculator

What Is a Good BMI for My Age? 

A healthy body mass index (BMI) is not one size fits all. BMI calculation will depend on different factors, including age.

  • For adults, for example, a good BMI falls within the 18.5 to 24.9 range. 
  • For children and teenagers between the ages of 2 to 18, BMI is calculated based on age, gender, height, and weight.

What BMI Range Is Normal?

The BMI ranges are listed in the table below, which tells you what is considered a healthy, underweight, overweight, obese, or morbidly obese weight range.

Body Mass Index (BMI) Ranges Table
BMI Range What It Means
Below 18.5 You're underweight
Between 18.5 and 24.9   You're at a healthy weight
Between 25 and 29.9      You're in the overweight range
Between 30 and 39.9      You're in the obese range
40 or greater You're in the morbidly obese range

How Do We Calculate BMI?

BMI is calculated using the following formula:

The formula for BMI is as follows:

  • Multiply your weight in pounds by 705.
  • Then divide by your height in inches.
  • Divide this by your height in inches again.

What Is Body Mass Index (BMI) Calculator?

To use this calculator:

  1. The default BMI of 16.6 shown on the tool is for a 5'5" person who weighs 100 lbs.
  2. Use the switch on top to pick either metric or imperial measurements.
  3. Set the height and weight dials to match your own height and weight.
  4. View your BMI number at the center of the tool and see where you fall on the obesity chart.

BMI values are based on clinical data about averages for these measurements across a wide range of people.

The BMI calculator gives general ranges of healthy and unhealthy weights for adults based on their height. The calculator does not take into account individual conditions. For one thing, it does not distinguish fat from muscle, water, or bone. Therefore, it is much less helpful in identifying the risk of health problems related to weight.

This BMI calculator allows you to easily screen yourself for obesity or extra, unhealthy weight. If your results from the calculator aren't in the healthy range, don't worry too much. People with muscular builds may be classified as obese, even with a low body fat percentage and optimum health, simply because the BMI formula uses only two data points.

Doctors and researchers use the BMI formula to screen for obesity, but not to diagnose it, as the BMI is a relatively blunt instrument. It is defined as weight in kilograms divided by height in meters squared (kg/m2). It can also be calculated for weight in pounds and height in inches.

Body mass index is closely related to body fat percentage but is much easier to measure. Therefore, it is used by many primary care doctors to identify obesity. The greater your BMI, the higher your risk of developing health problems related to excess weight.

What Is a Healthy BMI for Women? 

A healthy BMI for women falls within the range of 18.5 to 24.9, just like it does for men because there isn't a separate BMI chart for women vs. men. Weight, however, is different for women because they tend to have more percentage of body fat when compared to men. BMI is just one way of looking at your overall health but is not the entire picture.

Other factors that may affect your BMI:

  • You are an athlete (your muscle mass can cause you to weigh more)
  • You are postmenopausal (you will have more body fat)
  • Non-white ethnicity: Women of Mexican descent tend to have more body fat, while women who are Black tend to have more muscle mass than white women or women of Mexican descent, which is not factored into BMI.

Is Waist Circumference (WC) Useful in Determining Obesity?

Waist measurement is also an important factor. People with apple or pot belly shapes, who tend to put on weight around their waist, have a higher risk of obesity-related health problems. This includes women with a waist measurement of greater than 35 inches and men with a waist measurement of greater than 40 inches.

This measurement in a child or adolescent correlates closely with the future risk of developing type 2 diabetes mellitus and related complications of the metabolic syndrome (high blood pressure, abnormal cholesterol or other fat levels, heart attack, stroke, and damage to eyes, heart, and kidneys). The assessment is made with a tape measure stretched across the widest abdominal girth (usually at or just below the level of the belly button, called the umbilicus). Any value over the 90% percentile for age and gender carries the highest risk.

What Are More Accurate Ways to Measure Body Fat Percentage?

Many health professionals agree that percentage of body weight that is fat is a good marker of obesity. Men with more than 25% fat and women with more than 32% fat are considered obese.

Body fat percentage is difficult to measure accurately, however. Special equipment is needed that is not found at most medical offices. The methods used at health clubs and weight-loss programs may not be accurate if not done properly. Inexpensive scales for home use that estimate body fat are now widely available. They may not be entirely accurate but are generally consistent, so they may be used over time to track one's progress.

Reviewed on 11/18/2022
References
https://www.nhs.uk/common-health-questions/lifestyle/what-is-the-body-mass-index-bmi/

https://health.clevelandclinic.org/bmi-for-women/

National Institutes of Health

Droyvold, W.B., et al. "Weight change and mortality: the Nord-Trondelag Health Study." Journal of Internal Medicine 257.4: 338-345.

Life Measurements, Inc. (www.bodpod.com)

Manson, J.E., et al. "A prospective study of obesity and risk of coronary heart disease in women." N Engl J Med. 322.13 March 29, 1990: 882-9.

Sjöström, Lars, et al. "Lifestyle, Diabetes, and Cardiovascular Risk Factors 10 Years after Bariatric Surgery." New England Journal of Medicine 351 Dec. 23, 2004: 2683-2693.

Switzerland. World Health Organization. "Global Database on Body Mass Index."

United States. Centers for Disease Control and Prevention. National Center for Health Statistics. "National Health and Nutrition Examination Survey." July 17, 2019. <http://www.cdc.gov/nchs/nhanes.htm>.

United States. Food and Nutrition Service. U.S. Department of Agriculture. "Dietary Guidelines for Americans." <https://www.fns.usda.gov/cnpp/dietary-guidelines-americans>.

United States. National Institutes of Health. "Bioelectric Impedance Analysis in Body Composition Measurement." <https://consensus.nih.gov/1994/1994bioelectricimpedancebodyta015pdf.pdf>.

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