What is BMI?
BMI stands for Body Mass Index. It is a simple calculation that compares a person's weight with their height. BMI has been used as a general screening measure for adults because it provides a quick way to place a person's weight into a broad category. The calculation itself is straightforward, but the number should always be interpreted in context.
Our BMI calculator uses your height and weight to calculate the result automatically. You can enter measurements in metric units, such as centimeters and kilograms, or imperial units, such as feet, inches, and pounds. The result is then compared with commonly used adult BMI categories.
BMI is useful as a starting point, but it does not tell the whole story about health. Two people can have the same BMI while having very different amounts of muscle, body fat, bone mass, or where their body fat is stored. That's why BMI is best viewed as one piece of information rather than a complete assessment of someone's health.
How BMI is calculated
For adults using metric measurements, BMI is calculated by dividing weight in kilograms by height in meters squared.
BMI = weight (kg) ÷ height² (m)
For example, a person who weighs 70 kilograms and is 1.70 meters tall would have a BMI of approximately 24.2. The calculator handles the conversion and calculation for you, so you only need to enter your measurements.
With imperial measurements, the calculation uses pounds and inches and includes the appropriate conversion factor. You do not need to perform that conversion manually when using this calculator.
Adult BMI categories
For adults, standard BMI categories are commonly divided into four broad ranges. These categories can help provide context for a calculated BMI, but they should not be treated as a diagnosis.
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 to 24.9 | Healthy weight |
| 25.0 to 29.9 | Overweight |
| 30.0 or higher | Obesity |
These ranges are intended for adults. BMI interpretation is different for children and teenagers because their bodies are still growing. A child's BMI is generally interpreted using age- and sex-specific growth charts rather than the adult categories shown above.
How to use this BMI calculator
Choose your units
Select Metric if you use centimeters and kilograms, or Imperial if you use feet, inches, and pounds.
Enter your height
Enter your current height using the selected measurement system. Use your actual height rather than an estimate whenever possible.
Enter your weight
Enter your current body weight in kilograms or pounds.
Review the result
Your BMI number and category will appear immediately. Use the result as a general screening reference rather than a complete measure of health.
What does your BMI number mean?
A BMI below 18.5 falls in the underweight category under the standard adult classification. A BMI from 18.5 through 24.9 falls in the healthy-weight category. A result from 25.0 through 29.9 is classified as overweight, while a BMI of 30 or above falls in the obesity category.
These categories do not automatically mean that someone is healthy or unhealthy. BMI does not distinguish between muscle and fat, and it does not show where fat is distributed throughout the body. A muscular person, for example, may have a higher BMI because of greater muscle mass without having the same body-fat level as another person with the same BMI.
Age, sex, genetics, activity level, medical history, medications, and other factors can also matter when evaluating health and body composition. If you are concerned about your weight or BMI, a healthcare professional can help interpret the result alongside other relevant information.
BMI and healthy weight
People often use a BMI calculator when they are trying to understand whether their current weight falls within a commonly used range for their height. It can also be used as a simple starting point when tracking changes over time.
If your BMI changes, that does not necessarily mean your overall health has changed by the same amount. For example, changes in muscle mass, hydration, or other body-composition factors may affect body weight. Looking at a single BMI result without context can therefore be misleading.
A more useful approach is often to consider BMI alongside other measures and personal circumstances. Depending on your goals, a healthcare professional may consider waist measurements, blood pressure, blood tests, lifestyle, medical history, and other indicators when evaluating health.
BMI limitations
BMI is intentionally simple, which is both its strength and its limitation. Because it uses only height and weight, it cannot directly measure body fat or tell you how much of your weight comes from muscle, bone, organs, or fat.
- BMI does not directly measure body-fat percentage.
- BMI does not show where body fat is stored.
- A higher BMI can occur in people with substantial muscle mass.
- Adult BMI categories are not designed for children and teenagers.
- BMI alone cannot diagnose a health condition.
BMI for children and teenagers
The adult BMI categories on this page should not be used to interpret a child's or teenager's BMI. Younger people are still growing, and body composition changes with age and development.
For children and adolescents, BMI is generally compared with age- and sex-specific reference charts. If you need to evaluate a child's weight or growth, use a pediatric growth assessment or speak with a qualified healthcare professional rather than applying the adult categories directly.
Frequently asked questions about BMI
What is a normal BMI?
For adults, a BMI from 18.5 to 24.9 is commonly classified as healthy weight. This is a screening category and does not by itself determine whether someone is healthy.
How accurate is a BMI calculator?
The mathematical calculation is straightforward when accurate height and weight are provided. The limitation is interpretation: BMI is only a screening measure and does not directly measure body fat or overall health.
Does BMI work for muscular people?
BMI can be less informative for people with substantial muscle mass because the calculation cannot distinguish muscle from fat. A higher BMI does not necessarily mean that a muscular person has excessive body fat.
Can I calculate BMI in pounds and feet?
Yes. Select Imperial units and enter your height in feet and inches and your weight in pounds. The calculator handles the necessary conversion automatically.
Is BMI the same for men and women?
The standard adult BMI calculation uses the same formula for men and women. However, BMI does not account for differences in body composition, so the number should be considered alongside other relevant health information.
Should children use this BMI calculator?
The adult BMI categories shown here should not be used for children or teenagers. Their BMI is generally interpreted using age- and sex-specific growth references.
What should I do if my BMI is high or low?
A BMI outside the standard healthy-weight category does not automatically mean that something is wrong. Consider the result alongside your overall health and personal circumstances. A healthcare professional can provide individual guidance if you have concerns.
Does this calculator store my measurements?
The BMI calculation on this page runs directly in your browser. The calculator does not need to send your height or weight to a server to perform the calculation.
Health information disclaimer
This BMI calculator is provided for general informational purposes only. BMI is a screening measure and is not a medical diagnosis. It should not be used by itself to make decisions about treatment, medication, diet, or other medical care. If you have concerns about your weight, growth, or health, consult a qualified healthcare professional.