What is BMI?
Body Mass Index (BMI) is a simple screening number calculated from your height and weight. The formula is weight in kilograms divided by height in metres squared (kg/m²). It gives a quick indication of whether you are underweight, at a healthy weight, overweight, or obese for your height.
BMI categories (WHO)
Below 18.5 is considered underweight, 18.5 to 24.9 is a healthy weight, 25 to 29.9 is overweight, and 30 or above is classified as obese. These thresholds apply to most adults aged 20 and over.
Limitations of BMI
BMI does not distinguish between muscle and fat, so very muscular people may register as overweight despite low body fat. It is a general guide, not a diagnosis — always consult a healthcare professional for a full assessment.
Frequently asked questions
How is BMI calculated?
BMI equals your weight in kilograms divided by the square of your height in metres. In imperial units, multiply pounds by 703 and divide by height in inches squared.
What is a healthy BMI?
For most adults, a BMI between 18.5 and 24.9 is considered healthy.
Is BMI accurate for athletes?
Not always. BMI can overestimate body fat in muscular individuals and underestimate it in older adults with less muscle.
Does BMI differ for men and women?
The standard adult BMI thresholds are the same for men and women, though body composition and healthy ranges can differ.