What is a healthy BMI?

For most adults, 18.5 to 24.9 is classified as healthy weight by the World Health Organization. It is a population range, not a personal target.

Is BMI accurate for athletes?

Often not. Muscle is denser than fat, so a lean, muscular person can register as overweight on BMI while having a low body fat percentage.

How do I calculate BMI by hand?

Divide weight in kilograms by height in metres squared. In US units, multiply pounds by 703 and divide by height in inches squared.

Should BMI be interpreted differently by ethnicity?

Some health bodies apply lower overweight and obesity thresholds for people of South Asian, Chinese and other Asian descent, because cardiometabolic risk rises at a lower BMI in these groups.

What should I look at instead of BMI?

Waist circumference, waist-to-height ratio and a body fat estimate add information BMI cannot provide. A clinician can interpret them together.

BMI Calculator

Calculate body mass index in metric or US units, with categories and a healthy-weight range.

Enter your details and your result will appear here.

What Is BMI?

Body mass index is a ratio of weight to height used to place adults into broad weight categories. This calculator returns your BMI, the category it falls in and the weight range that corresponds to a BMI of 18.5 to 24.9 for your height.

Understanding Your BMI Result

BMI was designed by Adolphe Quetelet in the 1830s as a population statistic and later adopted for individual screening. It compares your weight to the square of your height, which means it scales roughly with body size but says nothing about what that weight is made of. Two people with the same BMI can differ substantially in fat mass, muscle mass and where fat is stored, which is why clinicians use it alongside waist circumference and other measures rather than on its own.

How Is BMI Calculated?

BMI = weight (kg) / height (m)^2

Methodology

BMI is weight in kilograms divided by height in metres squared. US inputs are converted first: pounds are multiplied by 0.45359237 and inches by 2.54. Categories follow the World Health Organization adult classification: under 18.5 underweight, 18.5-24.9 healthy weight, 25.0-29.9 overweight and 30.0 or above obesity.

Worked Example

Someone who is 5 ft 9 in (1.7526 m) and 175 lb (79.4 kg) has a BMI of 79.4 / (1.7526 x 1.7526) = 25.8, which sits in the overweight category. For that height, a BMI of 18.5 to 24.9 corresponds to roughly 125 to 169 lb.

Important Limitations

BMI does not measure body fat and does not distinguish muscle from fat, so athletes and muscular people are often classified as overweight while carrying little fat. It can also understate risk in older adults who have lost muscle. Risk thresholds differ across ethnic groups; lower cut-offs are used for some South and East Asian populations. It is not valid for children, pregnant people or those with significant fluid retention, and it is a screening tool rather than a diagnosis.

Frequently Asked Questions

What is a healthy BMI?: For most adults, 18.5 to 24.9 is classified as healthy weight by the World Health Organization. It is a population range, not a personal target.
Is BMI accurate for athletes?: Often not. Muscle is denser than fat, so a lean, muscular person can register as overweight on BMI while having a low body fat percentage.
How do I calculate BMI by hand?: Divide weight in kilograms by height in metres squared. In US units, multiply pounds by 703 and divide by height in inches squared.
Should BMI be interpreted differently by ethnicity?: Some health bodies apply lower overweight and obesity thresholds for people of South Asian, Chinese and other Asian descent, because cardiometabolic risk rises at a lower BMI in these groups.
What should I look at instead of BMI?: Waist circumference, waist-to-height ratio and a body fat estimate add information BMI cannot provide. A clinician can interpret them together.