Body Mass Index (BMI) Calculator
Body Mass Index (BMI) is a simple screening tool that estimates body fat based on your height and weight. Developed by Belgian mathematician Adolphe Quetelet in the 19th century, BMI is widely used by healthcare professionals as a quick indicator of whether a person falls into an underweight, normal weight, overweight, or obese category.
While BMI is a useful starting point for assessing health risks related to weight, it does not directly measure body fat or account for factors like muscle mass, bone density, age, or gender. Athletes with high muscle mass may have a high BMI despite having low body fat. For a more complete picture, BMI should be considered alongside other measurements such as waist circumference, body fat percentage, and overall fitness level.
How it works
BMI = weight (kg) / height (m)², where a result of 18.5–24.9 is considered normal weight, below 18.5 is underweight, 25–29.9 is overweight, and 30 or above is obese.
Use cases
- Quick health screening during routine medical checkups
- Tracking weight management progress over time
- Assessing population-level obesity trends in public health studies
- Setting baseline health goals for fitness programs
Frequently asked questions
How do I calculate my BMI?
Divide your weight in kilograms by your height in meters squared: BMI = weight (kg) / height (m)². For example, a person weighing 70 kg with a height of 1.75 m has a BMI of 70 / (1.75)² = 22.9, which falls in the normal weight range. Using pounds and inches, the equivalent formula is BMI = 703 × weight (lb) / height (in)².
What is a healthy BMI range?
A BMI between 18.5 and 24.9 is considered normal weight for adults. Below 18.5 is classified as underweight, 25 to 29.9 as overweight, and 30 or above as obese. These categories are the standard reference ranges used by the World Health Organization.
Is BMI accurate for athletes and muscular people?
Not always. BMI does not distinguish between muscle and fat, so athletes with high muscle mass can register as overweight or even obese despite having low body fat. For muscular individuals, complementary measures such as waist circumference or body fat percentage give a more accurate picture.
What BMI is considered obese?
A BMI of 30 or above is classified as obese. Obesity is commonly subdivided into class I (30–34.9), class II (35–39.9), and class III (40 or above). A BMI between 25 and 29.9 is classified as overweight, not obese.
Is the BMI formula different for men and women?
No. The formula BMI = weight (kg) / height (m)² and the standard categories are the same for adult men and women. However, BMI does not account for differences in body composition between genders, which is one of its known limitations.