BMI Calculator

What Is BMI?

BMI is a simple test that can tell if your weight is in a healthy range for your height. It's determined by dividing your body weight in kilograms by the square of your height in meters (or pounds by the square of your inches and multiplying by 703 for pounds and inches).

BMI doesn't measure body fat directly. The measurement is a screening measure rather than a diagnostic measure, and it is usually combined with other test results (waist circumference, blood pressure, cholesterol and health history) to help health care providers understand more about an individual's health.

BMI Formula

• Metric: Body Mass Index (BMI) = weight (kg) ÷ height (m)²
• Imperial: BMI = [weight (lb) ÷ height (in)²] × 703

Worked example: A person who is 5'7" (67 inches) and weighs 160 lb: BMI = 703 × [160 ÷ (67 × 67)] = 703 × [160 ÷ 4,489] = 703 × 0.0356 = 25.1. This puts this example in the "overweight" range of the standard adult BMI scale below.

BMI Categories for Adults

The following is the normal BMI range for adults (aged 20 and above) for both men and women, according to the World Health Organization (WHO):

For clinical use, obesity is sometimes broken down into three sub-classes (Class 1: 30 – 34.9, Class 2: 35 – 39.9, Class 3: ≥ 40).

Instructions for using this BMI calculator

• Choose your preferred unit system (metric or imperial).
• Enter your current weight and height.
• Your BMI and category will calculate instantly.

There is no log-in, download or personal information required and anything entered will not be stored or shared.

BMI for Children and Teens is Different

There are no adult BMI categories for children and teens, as amounts of body fat that are ‘normal' and ‘healthy' vary with age and gender as children grow. BMI is then remediated to an age- and sex-specific percentile value, placing children's BMI in comparison to BMI values of other children of the same age and sex (not to a fixed range). For children and teenagers, use a BMI-for-age calculator instead of the adult ranges on this page when calculating BMI.

Limitations of BMI

BMI is a helpful starting point but has actual limitations with well documented evidence that should be understood prior to making a single number judgment:

• Not selective on muscle or fat: Athletes and highly muscular people tend to be classified as "overweight" or "obese", although their body fat is low, but their muscle mass is higher.
• Does not take into consideration fat distribution: Visceral (abdominal) fat carries different health risk and can be different amounts of fat for two people with the same BMI.
• May not be as accurate for seniors: A higher level of BMI (25-27) is sometimes seen as acceptable for individuals who are over 65 years old, as these people tend to lose muscle and bone density.
• Standardized mainly on data from whites: Some countries have guidelines for Asian BMI that are lower than the WHO standard, for example, a BMI of 23 is already classified as "at risk" in several Asian countries, whereas 25 is classified as "at risk" in the WHO standard. Research suggests standard BMI categories might be more likely to overestimate the risk in Black persons and underestimate the risk in people of Asian descent.
• Don't call it a diagnosis! BMI has its limits as an indicator of metabolic health, with a healthy weight BMI not necessarily being healthy, and a poor health BMI not necessarily being unhealthy.

Having a BMI that falls outside the "healthy weight" category means that the next step is a discussion with a healthcare provider or doctor, not a diagnosis based on that number.

Why BMI is still widely used

In spite of its flaws, BMI is the accepted initial screening measure in clinical, insurance, and public health practice for a very practical reason: It's easy to calculate, doesn't cost a dime, and doesn't require a special device to do so (unlike body fat percentage, which typically does involve specialized equipment like DEXA scans, skinfold calipers, or bioelectrical impedance devices). It's used as a starting point, not a final answer, because of that accessibility.

Ponderal Index Explained

Unlike standard BMI which scales weight against height squared, the Ponderal Index (PI) divides weight by height cubed. PI scales mass three-dimensionally, providing more balanced, accurate body metric calculations for taller or shorter individuals.

Ideal Calorie Targets (BMR)

Your BMR (Basal Metabolic Rate) represents the baseline calories burned by vital life processes while resting. The calculator applies the Mifflin-St Jeor formula and multiplies it by standard active modifiers (defaulting to lightly active) to evaluate caloric targets for stable weight maintenance, calorie deficit loss, or calorie surplus gains.

Frequently Asked Questions