About this calculator
Body mass index is the most widely used weight screening tool in the world because it needs only height and weight. It works well as a population-level indicator, and poorly as an individual assessment, since it cannot tell muscle from fat.
How it works
BMI is weight in kilograms divided by height in metres squared. The imperial formula is 703 × weight in pounds divided by height in inches squared. The resulting number is compared against standard adult categories.
Frequently asked questions
How do I calculate my BMI?
BMI = weight (kg) ÷ height (m)². In imperial units, BMI = 703 × weight (lbs) ÷ height (in)². The result is a number between about 10 and 60 for most adults.
What are the BMI categories?
Under 18.5 is underweight, 18.5 to 24.9 is healthy weight, 25 to 29.9 is overweight, and 30 or above is classified as obese. These apply to adults aged 20 and over.
Is BMI accurate for everyone?
Not really. It cannot distinguish muscle mass from fat, so muscular athletes often read as overweight. It is also less accurate for children, the elderly, and people with very different body proportions from the population average.
What is a healthy BMI for my height?
For most adults, a BMI between 18.5 and 24.9. Multiply your height in metres by 18.5 and by 24.9 to get the weight range in kilograms that corresponds to that band.
Why does my BMI differ from my doctor’s assessment?
Your doctor considers body composition, fat distribution, muscle mass, bone density, and medical history. BMI is one screening number among many, and a low or high reading alone does not establish a diagnosis.
How much weight should I lose to reach a healthy BMI?
Work out the difference between your current weight and the midpoint of the healthy range for your height, then aim for 0.5 to 1 kg per week. Gradual change is more sustainable and protects muscle.