BMI Calculator – Check Your Body Mass Index
Calculate your Body Mass Index (BMI) instantly. Enter your height and weight to find out if you're underweight, normal, overweight, or obese.
How BMI is Calculated
Body Mass Index (BMI) is calculated by dividing your weight in kilograms by the square of your height in meters: BMI = weight(kg) / height(m)².
For example, if you weigh 70 kg and are 1.75 m tall, your BMI would be 70 / (1.75 × 1.75) = 22.9.
BMI was devised in the 1830s by Belgian mathematician Adolphe Quetelet and remains the most widely used screening tool for weight categories worldwide.
BMI Categories
- Underweight: BMI below 18.5
- Normal weight: BMI 18.5 to 24.9
- Overweight: BMI 25.0 to 29.9
- Obese Class I: BMI 30.0 to 34.9
- Obese Class II: BMI 35.0 to 39.9
- Obese Class III: BMI 40.0 and above
These categories are defined by the World Health Organization (WHO) and are used globally as a screening tool. However, cutoff points may vary for different ethnic groups — for example, Asian populations may have higher health risks at lower BMI values.
Limitations of BMI
BMI is a useful screening tool but has significant limitations:
- Muscle mass: Athletes and bodybuilders may have a high BMI due to muscle, not fat
- Age: Older adults tend to have more body fat than younger adults at the same BMI
- Sex: Women typically have more body fat than men at the same BMI
- Bone density: People with denser bones may weigh more without excess fat
For a more complete picture of your health, consider combining BMI with waist circumference measurements, body fat percentage, and other health markers.
Frequently Asked Questions
What is a healthy BMI?
A healthy BMI falls between 18.5 and 24.9 according to the WHO. This range is associated with the lowest risk of weight-related health problems. However, individual health depends on many factors beyond BMI.
Is BMI accurate for athletes?
BMI can be misleading for athletes and muscular individuals. Since muscle weighs more than fat, a fit person with significant muscle mass may have a BMI in the overweight range despite having low body fat. Body fat percentage is a better metric for athletes.
How often should I check my BMI?
For most adults, checking BMI once or twice a year is sufficient unless you are actively trying to lose or gain weight, in which case monthly tracking can help monitor progress.