Calculate Your BMI

How the BMI Calculator Works

The BMI calculator uses your height and weight to produce a body mass index number.

The calculation adjusts weight for height, which makes it more useful than looking at body weight alone. A person who weighs 180 pounds at one height may receive a different BMI result from someone who weighs the same amount but is taller or shorter.

The calculator then compares the result with standard adult BMI ranges.

BMI is widely used because it is:

• Quick to calculate
• Easy to understand
• Inexpensive
• Useful for general screening
• Suitable for comparing large groups

Its simplicity also creates limitations. The calculator cannot determine whether weight comes from fat, muscle, bone, fluid, or another source.

BMI Formula

The calculation depends on the measurement system selected.

Metric BMI Formula

US BMI Formula

For more worked examples, read our complete BMI formula guide.

What Does Your BMI Result Mean?

Your BMI result shows how your weight compares with your height. The number is then grouped into a standard adult BMI category. This can help identify whether your weight falls below, within, or above the usual screening range.

The result may be useful for:

• Initial health screening
• Tracking changes over time
• Discussing weight-related concerns
• Comparing weight with height
• Identifying when further assessment may be useful

However, the result cannot explain why your BMI falls within a particular category.

A higher BMI may reflect:

• Higher body fat
• Greater muscle mass
• A larger body frame
• Age-related body changes
• Fluid retention
• Pregnancy
• Other personal factors

A lower BMI may also have several possible explanations. The number should always be read in context.

What BMI Does Not Measure

BMI is based only on height and weight. It does not directly measure:

• Body fat percentage
• Muscle mass
• Bone density
• Waist circumference
• Fat distribution
• Abdominal fat
• Fitness level
• Strength
• Nutrition quality
• Blood pressure
• Blood sugar
• Cholesterol
• Medical conditions
• Overall health

This means two adults with the same BMI can have very different body composition and health profiles.

One person may have more muscle and less body fat. Another may have less muscle and more abdominal fat. Their BMI number could still be identical.

Read more about the limitations of BMI.

When BMI May Be Less Accurate

BMI can be useful for many adults, but it may require extra context for certain groups.

Athletes and Muscular Adults

Muscle is denser than body fat. People with substantial muscle mass may receive an overweight or obesity BMI result even when their body fat level is not high.

BMI does not distinguish between fat and muscle. Read more about BMI for athletes.

Older Adults

Adults may lose muscle mass as they age. This means an older person can have a BMI within the healthy range while carrying less muscle and more body fat than the number suggests.

See our guide to BMI for seniors.

Pregnant Adults

Standard BMI calculations are not designed to interpret weight changes during pregnancy.

Pre-pregnancy BMI may sometimes be used as part of pregnancy guidance, but current pregnancy weight should be discussed with a qualified healthcare professional.

Children and Teenagers

Adult BMI categories do not apply to people under age 20. Children and teenagers are assessed using BMI-for-age percentiles that account for age and sex.

Some Ethnic Groups

Research and health guidance may use lower BMI thresholds for certain populations because health risks can occur at different BMI levels.

BMI should therefore be considered alongside personal background and clinical information. Read about BMI for Asian adults.

Other Measurements to Consider

BMI can provide a starting point, but other measurements may add useful context.

Waist Circumference

Waist size can help show where fat is stored. Fat around the abdomen may be associated with different health risks than fat stored elsewhere.

Waist-to-Height Ratio

Waist-to-height ratio compares waist size with height. It can provide additional information about central fat distribution.

Body Fat Percentage

Body fat percentage estimates how much of the body consists of fat. Results can vary depending on the measurement method.

Blood Pressure

Blood pressure provides information that BMI cannot show. A person can have a BMI within the healthy range and still have high blood pressure.

Blood Sugar and Cholesterol

Blood tests may provide a clearer view of some metabolic and cardiovascular risk factors than BMI alone.

No single measurement gives a complete picture. BMI is most useful when considered with other health information.

What to Do After Checking Your BMI

Your next step depends on why you used the calculator and what concerns you may have.

If Your BMI Falls Within the Healthy Weight Range

Continue looking at the wider picture. Consider:

• Regular movement
• Balanced nutrition
• Sleep
• Stress
• Blood pressure
• Blood sugar
• Cholesterol
• Waist size
• Medical history

A healthy-range BMI does not guarantee that every other health measure is within a healthy range.

If Your BMI Is Below the Healthy Weight Range

A lower BMI does not always mean there is a problem. However, consider professional guidance if you have:

• Unexplained weight loss
• Ongoing fatigue
• Loss of appetite
• Nutritional concerns
• Digestive symptoms
• A medical condition affecting weight

If Your BMI Is Above the Healthy Weight Range

A higher BMI does not automatically mean you are unhealthy. Consider looking at:

• Waist circumference
• Recent weight changes
• Activity level
• Blood pressure
• Blood sugar
• Cholesterol
• Sleep quality
• Family history
• Existing health conditions

A qualified healthcare professional can help you understand the result in a more personal context.