Body Mass Index is the most widely used screening tool for weight-related health risks. Here is everything you need to know about what your BMI number means, its limitations, and when to pay attention to it.
What Is BMI?
BMI is calculated by dividing your weight by your height squared. The formula in imperial units is: BMI = (weight in pounds × 703) ÷ (height in inches)². A 5'10" person weighing 170 lbs has a BMI of 24.4 — just within the normal range.
BMI Categories
The World Health Organization defines four categories: Underweight (below 18.5), Normal weight (18.5-24.9), Overweight (25-29.9), and Obese (30+). These ranges were established based on large population studies linking BMI to health risks like heart disease, diabetes, and certain cancers.
Why BMI Has Limitations
BMI does not distinguish between muscle and fat. A bodybuilder and an obese person of the same height and weight have identical BMIs despite very different health profiles. BMI also does not account for age, gender, ethnicity, or where fat is distributed on the body. Waist circumference is actually a better predictor of health risk than BMI alone.