Body Mass Index (BMI) is a widely used screening tool that estimates whether a person has a healthy body weight relative to their height. While it is not a perfect measure, BMI provides a useful starting point for understanding your overall health and potential weight-related risks.
This guide explains how BMI is calculated, what the numbers mean, and how to use our free BMI calculator as part of a broader approach to health and wellness.
BMI is calculated by dividing your weight in kilograms by the square of your height in meters. The formula is simple: BMI = weight (kg) / height (m). For imperial measurements, the formula is BMI = (weight in pounds / height in inches) times 703.
Our body mass index calculator supports both metric and imperial units, making it easy for anyone to get their BMI instantly. Simply enter your height and weight, and the calculator does the rest, showing your BMI value and weight category.
The World Health Organization defines the following BMI categories for adults:
While BMI is a useful screening tool, it has several important limitations. BMI does not distinguish between muscle mass and fat mass. This means muscular athletes may be classified as overweight or obese despite having very low body fat. Conversely, older adults who have lost muscle mass may have a normal BMI while having excess body fat.
BMI also does not account for where fat is distributed on your body. Visceral fat (fat stored around your organs) is more harmful than subcutaneous fat (fat under the skin). Waist circumference is often used alongside BMI to provide a more complete picture. A waist measurement of over 40 inches (102 cm) for men or 35 inches (88 cm) for women indicates increased health risk regardless of BMI.
For a more complete health assessment, consider tracking these additional metrics alongside your BMI:
If your BMI falls outside the normal range, making sustainable lifestyle changes is the most effective approach. Focus on a balanced diet rich in whole foods, vegetables, lean proteins, and healthy fats. Aim for at least 150 minutes of moderate-intensity exercise per week, including both cardio and strength training.
Set realistic goals. Losing just 5% to 10% of your body weight can significantly improve health outcomes, even if you do not reach an ideal BMI. Track your progress with our BMI calculator free tool to see how your numbers change over time as you make healthier choices.