Body Mass Index or BMI is a calculation that is used to understand the relationship between your height and weight. It is very commonly used in healthcare settings and also in gyms or weight training centers. It helps fitness coaches and healthcare professionals to categorize people as underweight, normal weight, overweight, or obese. The goal of BMI is to get a rough estimate of body fat, which can then highlight potential risks for chronic health problems. But while BMI is easy to calculate and useful as a general guideline, it doesn’t tell the full story of a person’s health.How Is BMI Calculated?The formula for BMI differs slightly depending on the measurement system you use.Metric: BMI = weight (kg) ÷ height (m²)Imperial: BMI = (weight in pounds ÷ height in inches²) × 703For example, someone who weighs 180 pounds and is 5 feet 6 inches tall (66 inches) would have a BMI of:(180 ÷ 66²) × 703 = 29.0That would place them in the "overweight" category.BMI is also divided into these categories that then determine where the person falls under the spectrum from underweight to obesity:Underweight: less than 18.5Normal: 18.5 – 24.9Overweight: 25.0 – 29.9Obesity Class 1 (mild): 30.0 – 34.9Obesity Class 2 (moderate): 35.0 – 39.9Obesity Class 3 (severe): 40.0 or higherGenerally, the higher your BMI, the greater your risk of health conditions such as heart disease, type 2 diabetes, high blood pressure, sleep apnea, fatty liver, and even certain cancers.Is BMI Reliable?While BMI is not a diagnostic test, it can be a helpful screening tool. It is used to track trends in population, raise awareness of weight-related risks, and to initiate conversations between patients and healthcare providers. However, BMI often leaves out the muscle mass, bone structure, or fat distribution. One of the most common example is when an athlete with high muscle mass is classified as "overweight" despite having a low body fat. This is why, there are other ways to measure too, including: Waist CircumferenceExcess belly fat is a stronger risk factor than fat stored elsewhere.High risk:Men: waist > 40 inchesWomen: waist > 35 inchesBody Composition AnalysisTools like InBody or SECA scales provide a breakdown of fat mass, muscle, and water weight—offering more detail than BMI.DEXA ScanThis scan is the gold standard for measuring body fat, bone density, and fat distribution—but it’s expensive and not widely available.Metabolic Health MarkersLab tests like fasting glucose, cholesterol levels, and inflammation markers help assess overall health more accurately than BMI alone.BMI could also vary depending on your ethnicity. More South Asians are risk for diabetes and heart disease at lower BMIs. For them, "overweight" may begin at 23 and "obese" at 25. African Americans may have higher muscle mass and lower visceral fat, which can cause BMI to overestimate health risks. Hispanic and Indigenous populations may carry more risk at lower BMIs due to genetic factors.While it is important to care about your BMI, however, it should not be the only way to measure your health. You must also consider waist size, body composition, fitness level, blood test results, and ethnic background.