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BMI Calculator

Body mass index (BMI) is weight in kilograms divided by height in metres squared. For adults, under 18.5 is underweight, 18.5 to 24.9 is a healthy weight, 25 to 29.9 is overweight and 30 or more is obesity. A person who is 176 cm and 72 kg has a BMI of 23.2.

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BMI23.2Healthy weight
Healthy range for your height57.3 to 77.1 kg

BMI = weight (kg) ÷ height (m)². WHO adult categories.

How to use the BMI Calculator

  1. Enter your weight and choose kg or lb.
  2. Enter your height and choose cm or inches.
  3. Read your BMI and WHO category, which update as you type.
  4. Check the healthy weight range shown for your height and the position on the scale.

Formula

BMI = weight (kg) ÷ height (m)² · imperial: BMI = 703 × weight (lb) ÷ height (in)²

Pounds and inches are converted to kilograms and centimetres before calculating. The healthy range shown is the weight that gives a BMI of 18.5 to 24.9 at your height. Categories follow the World Health Organization adult cut-offs.

Adult BMI categories (WHO)

  • Underweight: below 18.5
  • Healthy weight: 18.5 to 24.9
  • Overweight: 25 to 29.9
  • Obesity class I: 30 to 34.9
  • Obesity class II: 35 to 39.9
  • Obesity class III: 40 and above

What BMI does not measure

BMI is a screening tool, not a diagnosis. It does not separate muscle from fat, so muscular athletes can score as overweight, and older adults with low muscle mass can score as healthy while carrying excess fat. It is not used for children, teens or pregnancy. Waist size or a body fat estimate adds useful context.

BMI Calculator questions

What is BMI and why is it used?

BMI (body mass index) is a ratio of weight to height squared that estimates whether a person's weight is in a healthy range for their height. It is quick, free and needs no equipment, so doctors use it to screen for health risks linked to being underweight, overweight or obese.

What are the BMI categories and ranges?

For adults: underweight is below 18.5, healthy weight is 18.5 to 24.9, overweight is 25 to 29.9, and obesity is 30 and above. Obesity is further split into class I (30 to 34.9), class II (35 to 39.9) and class III (40 and above).

How do I calculate my BMI manually?

Divide your weight in kilograms by your height in metres squared. For 72 kg and 1.76 m: 72 ÷ (1.76 × 1.76) = 23.2. In imperial units, multiply weight in pounds by 703 and divide by height in inches squared: a 5 ft 6 in person weighing 150 lb has a BMI of 24.2.

Is BMI accurate for everyone?

No. BMI is a useful screening tool but it cannot tell muscle from fat. It can overestimate fatness in athletes and muscular people and underestimate it in older adults who have lost muscle. It is not designed for children, teens, or pregnant women.

What BMI should I aim for?

For most adults, a BMI between 18.5 and 24.9 is considered healthy. Within that range, other markers such as waist size, blood pressure, blood sugar, cholesterol and fitness matter more than an exact BMI number. The calculator shows the weight range that keeps you within it.

Does BMI differ by age or sex?

The adult categories are the same for men and women aged 18 and over. Children and teens are assessed with age- and sex-specific BMI percentiles instead. Some research suggests slightly higher BMIs carry less risk for adults over 65, so interpretation can vary with age.

Can BMI predict my health risks?

BMI is linked to risk but does not diagnose anything. Higher BMI values are associated with type 2 diabetes, heart disease, high blood pressure and stroke, and very low values with nutrient deficiency and bone loss. Genetics, activity and diet also shape individual risk.

Is there a better measure than BMI?

Several measures add detail. Waist circumference and waist-to-height ratio show abdominal fat, which is closely tied to metabolic risk. Body fat percentage separates fat from lean mass. Used together with BMI, they give a clearer picture than any single number.

What should I do if my BMI is too high or too low?

Talk to a doctor or registered dietitian before making big changes. They can check whether the number reflects body fat or muscle, look at other health markers, and suggest a safe plan for diet, activity or medical support based on your circumstances.