BMI Calculator
Calculate your Body Mass Index from your height and weight and see the corresponding adult BMI category.
How to Interpret Your Result
What Is BMI?
BMI stands for Body Mass Index. It is a calculation that compares body weight with height.
BMI is widely used as a quick screening measure because it requires only two simple measurements: height and weight.
For an individual adult, BMI can provide one piece of information about weight relative to height, but it should not be treated as a complete assessment of health or body composition.
How Is BMI Calculated?
BMI is calculated by dividing weight in kilograms by height in meters squared.
Metric BMI Formula
Example
When pounds and feet are entered, this calculator converts the measurements to kilograms and meters before applying the same BMI formula.
Adult BMI Categories
Adult BMI results are commonly divided into the categories shown below.
| BMI Range | Adult Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 to 24.9 | Healthy Weight |
| 25.0 to 29.9 | Overweight |
| 30.0 to 34.9 | Obesity Class 1 |
| 35.0 to 39.9 | Obesity Class 2 |
| 40.0 or higher | Obesity Class 3 |
BMI Calculation Example
Consider an adult who weighs 75 kilograms and is 170 centimeters tall.
170 cm = 1.70 m
Step 2 — Square the height1.70 × 1.70 = 2.89
Step 3 — Divide weight by height²75 ÷ 2.89 ≈ 25.95
How Does the BMI-Based Weight Range Work?
Once height is known, the BMI formula can be rearranged to calculate the body weights that correspond to particular BMI values.
This calculator uses BMI 18.5 for the lower end and BMI 24.9 for the upper end of the displayed adult healthy-weight reference range.
The result should not be interpreted as a requirement to reach a particular scale weight. It is simply the range of body weights corresponding mathematically to those BMI values.
Limitations of BMI
BMI is convenient, but it cannot show how much of your body weight comes from muscle, fat, bone, or other tissue.
Does Not Measure Body Fat Directly
BMI is calculated from height and weight rather than directly measuring body fat.
Does Not Separate Muscle and Fat
Two people with the same BMI can have substantially different body composition.
Does Not Show Fat Distribution
BMI does not indicate where body fat is carried.
Is Not a Diagnosis
BMI should be considered with other health information, not used by itself to diagnose disease.
BMI After Age 50
The adult BMI formula does not change when a person turns 50. Height and weight are still used in exactly the same calculation.
What can change with age is body composition. A person's amount of muscle and body fat can change even when body weight remains fairly stable.
For that reason, adults over 50 may find it useful to think about BMI alongside factors such as muscle mass, strength, mobility, waist measurements, physical activity, blood pressure, laboratory results, and overall health.
BMI vs. Body Fat Percentage
Body Mass Index
Uses only total body weight and height to create a screening number.
Body Fat Percentage
Attempts to estimate how much of total body weight consists of fat tissue.
They are related concepts but are not interchangeable. A BMI calculator does not directly calculate body fat percentage.
What Else Should Be Considered With BMI?
A more complete assessment of health may consider BMI together with other information.
- Medical history and existing health conditions
- Blood pressure
- Blood glucose and cholesterol levels
- Muscle mass and physical strength
- Waist measurement and body-fat distribution
- Physical activity and fitness
- Nutrition and eating patterns
- Changes in weight over time
Why Doesn't the Adult BMI Calculator Ask for Age or Sex?
The standard adult BMI formula uses only height and weight. Age and sex are therefore not required to calculate the BMI number itself.
For adults age 20 and older, the same standard BMI category thresholds are used by this calculator.
This is different from BMI assessment for children and teenagers, where age- and sex-specific growth charts and percentiles are used.
How to Use Your BMI Result
Enter Accurate Measurements
Use a current weight and an accurate height measurement.
Review Your BMI
The calculator shows your BMI to one decimal place.
Check the Category
Compare your number with the standard adult BMI screening categories.
Consider the Bigger Picture
Use BMI alongside body composition, health history, physical function, and other relevant information.
Frequently Asked Questions
BMI stands for Body Mass Index. It is calculated from body weight relative to height.
The standard adult Healthy Weight BMI category is 18.5 to 24.9.
BMI does not directly measure body fat. It is a screening calculation based on height and weight.
Yes. BMI does not distinguish muscle from body fat, so a person with substantial muscle mass can have a relatively high BMI.
The standard adult BMI calculation itself does not change with age. However, age-related changes in body composition can affect how useful BMI is when considered by itself.
The standard adult BMI formula and category thresholds used here are the same for men and women. Body composition can still differ substantially between individuals with the same BMI.
No. BMI is a screening measure and should be considered alongside other health information.
This calculator is designed for adults age 20 and older. BMI interpretation for children and teenagers uses age- and sex-specific percentiles rather than the adult category system.
