BMI Calculator
Use our free BMI Calculator to quickly estimate your Body Mass Index (BMI) based on your height and weight. Enter your details to calculate your BMI and see which standard adult BMI category your result falls into.
BMI is a useful screening measure that compares your weight with your height. It can help you understand whether your current weight falls within a commonly used range, but it does not provide a complete picture of your health.
For the most meaningful result, enter your current height and weight as accurately as possible.
Important: BMI is a screening tool, not a medical diagnosis. Your BMI result should be considered alongside other factors such as muscle mass, waist measurement, medical history, physical activity, nutrition, and overall health.
<18.5 Normal
18.5–24.9 Overweight
25–29.9 Obese
≥30
What Is BMI?
BMI stands for Body Mass Index. It is a numerical value calculated using your body weight and height.
For adults, BMI is commonly used as a quick way to screen for weight categories that may be associated with certain health risks. The calculation uses your weight in kilograms and height in meters squared.
BMI Formula
BMI = Weight (kg) ÷ Height² (m)
For example, if an adult weighs 70 kg and is 1.75 meters tall:
BMI = 70 ÷ (1.75 × 1.75)
BMI = 22.9
This result falls within the standard healthy weight BMI category for adults.
The calculation itself is simple, but interpreting the result requires context. A BMI number should not be treated as a direct measurement of body fat or as a diagnosis of a health condition. The CDC describes BMI as a screening measure that should be considered alongside other health information.
How to Use Our BMI Calculator
Calculating your BMI takes less than a minute.
Step 1: Enter Your Height
Enter your height using the available unit options, such as feet and inches or centimeters/meters, depending on the calculator.
For the most accurate result, measure your height without shoes and avoid estimating if you can take an actual measurement.
Step 2: Enter Your Weight
Enter your current body weight in kilograms or pounds, depending on the unit selected.
For a more reliable result, use a reasonably accurate weighing scale and enter your current weight rather than an old measurement.
Step 3: Calculate Your BMI
Click the Calculate button to receive your BMI result.
Your result will show a BMI number that you can compare with the standard adult BMI categories below.
Step 4: Understand Your Result
Your BMI is only the starting point. Use your result to learn more about your weight status, then consider other factors that affect your health.
If you are concerned about your weight, have experienced unexplained weight changes, or have an existing health condition, speak with a qualified healthcare professional.
Adult BMI Categories
For adults, standard BMI categories are generally interpreted as follows:
| BMI Range | Category |
|---|---|
|
Below 18.5 |
Underweight |
|
18.5 to less than 25 |
Healthy Weight |
|
25 to less than 30 |
Overweight |
|
30 or higher |
Obesity |
The obesity category is further divided into:
| BMI Range | Obesity Class |
|---|---|
|
30 to less than 35 |
Class 1 |
|
35 to less than 40 |
Class 2 |
|
40 or higher |
Class 3 |
These categories are used for adults. BMI assessment for children and teenagers is different because it uses age- and sex-specific growth patterns and percentiles rather than the standard adult categories.
What Does My BMI Result Mean?
Your BMI category can give you a general indication of how your weight compares with your height.
BMI Below 18.5: Underweight
A BMI below 18.5 falls into the underweight category under standard adult BMI classifications.
Being underweight does not automatically mean that you have a health problem. However, unexplained weight loss or difficulty maintaining weight may deserve further attention.
If you are underweight and concerned about your health, consider discussing your weight, diet, and overall wellbeing with a healthcare professional.
BMI 18.5 to Less Than 25: Healthy Weight
This range is commonly classified as healthy weight for adults.
However, being within this BMI range does not guarantee that you are healthy. Your fitness level, diet, waist measurement, blood pressure, cholesterol, sleep, activity level, and other factors also contribute to your overall health.
Think of BMI as one piece of the health picture rather than a complete health score.
BMI 25 to Less Than 30: Overweight
A BMI in this range falls into the overweight category under standard adult classifications.
A higher BMI can be associated with an increased risk of certain health conditions, but BMI alone cannot determine your individual health risk.
Your healthcare provider may consider additional factors, including your waist measurement, medical history, lifestyle, and other health indicators.
BMI 30 or Higher: Obesity
A BMI of 30 or higher falls into the obesity category under standard adult classifications.
Higher levels of excess body weight can be associated with an increased risk of several chronic health conditions. However, BMI is still a screening measure and does not diagnose an individual health condition.
If your BMI falls within this category, consider discussing your result with a healthcare professional who can assess your overall health and help you choose appropriate next steps.
Is BMI Accurate?
BMI is useful because it is simple, fast, inexpensive, and easy to calculate. It works well as a broad screening tool for many adults.
However, BMI has important limitations.
BMI does not directly measure:
- Body fat percentage
- Muscle mass
- Bone density
- Fat distribution
- Waist circumference
- Overall fitness
- Dietary quality
- Blood pressure
- Blood sugar
- Cholesterol levels
For example, someone who regularly participates in strength training may have a higher BMI because of greater muscle mass. The BMI calculation cannot distinguish muscle from body fat.
On the other hand, a person can have a BMI within the standard healthy range while still having other health risks.
For this reason, a BMI result should always be interpreted in context. The CDC recommends considering BMI alongside factors such as medical history, health behaviors, physical examination findings, and laboratory results.
BMI Is Not the Same as Body Fat Percentage
This is one of the most important things to understand about BMI.
BMI estimates weight status based on height and weight. It does not directly measure how much body fat you have.
Two people can have exactly the same BMI but have very different body compositions.
For example:
- One person may have more muscle and less body fat.
- Another person may have less muscle and more body fat.
Both could have the same BMI even though their body composition is different.
If you want a more complete assessment of your body composition, other measurements may provide additional information. Depending on your goals, these may include waist circumference, waist-to-height ratio, skinfold measurements, bioelectrical impedance, or clinical body composition testing.
No single measurement tells the whole story.
BMI and Waist Measurement
Where your body stores fat can also matter.
BMI does not show whether a person’s weight is concentrated around the abdomen. A waist measurement can provide additional information about abdominal fat and may help provide a broader picture of health risk.
The NHS recommends considering waist measurement alongside BMI in appropriate circumstances. It also notes that waist-to-height ratio can help assess whether a person is carrying excess weight around the waist.
What Is a Healthy BMI?
For standard adult BMI classifications, a BMI from 18.5 to less than 25 is generally categorized as healthy weight.
However, the idea of a “healthy BMI” needs context.
Your ideal health target is not determined by BMI alone. Your age, muscle mass, lifestyle, medical history, family history, and other factors can influence your overall health.
A BMI number should therefore be used as a starting point for understanding your weight status rather than as a personal health diagnosis.
Does Age Affect BMI?
The standard adult BMI categories are generally used for adults regardless of age.
However, BMI should still be interpreted within the broader context of a person’s health. Factors such as changes in muscle mass, physical activity, medical conditions, and body composition can become increasingly relevant as people age.
For children and teenagers, do not use standard adult BMI categories. Their BMI is interpreted differently using age- and sex-specific growth references.
Does Gender Affect BMI?
The standard adult BMI categories are generally applied to adults without separate category thresholds based solely on sex.
However, BMI does not account for differences in body composition between individuals. Two adults with the same BMI may have different proportions of muscle and body fat.
This is another reason why BMI works best as one part of a broader health assessment rather than as a standalone measure.
BMI and Muscle-Building Athletes
If you lift weights, play sports, or have a high level of muscle mass, your BMI may be higher than expected.
Muscle is denser than fat, and BMI only considers your total weight in relation to your height. As a result, some muscular individuals may fall into the overweight or obesity category even when they have relatively low body fat.
If you have significant muscle mass, consider BMI alongside other measurements rather than relying on BMI alone.
How to Get a More Complete Picture of Your Health
Your BMI can be a useful first step, but you can learn more by looking at several health indicators together.
Depending on your situation, you may consider:
- BMI – Provides a weight-to-height screening measure.
- Waist measurement – Provides information about abdominal size.
- Waist-to-height ratio – Offers another way to consider abdominal fat.
- Body composition – Helps estimate the proportion of fat and lean mass.
- Blood pressure – Helps identify elevated blood pressure.
- Blood glucose – Provides information about blood sugar levels.
- Cholesterol – Helps assess cardiovascular risk factors.
- Physical activity – Shows how active you are in daily life.
- Diet quality – Considers the nutritional value of your usual food intake.
- Medical history – Adds important personal health context.
The best assessment combines relevant measurements rather than relying on one number.
What Should I Do After Calculating My BMI?
Your next step depends on your result and your personal circumstances.
If your BMI falls within the healthy weight category, focus on maintaining sustainable habits rather than trying to reach a specific number on the scale.
If your BMI is above or below the standard healthy range, avoid making sudden or extreme changes based only on the calculator result.
Instead, consider:
- Eating a balanced and varied diet.
- Staying physically active.
- Getting adequate sleep.
- Managing stress.
- Tracking gradual changes in your weight.
- Monitoring your waist measurement when appropriate.
- Speaking with a healthcare professional if you have concerns.
If you are trying to lose or gain weight, aim for sustainable changes that you can maintain over time. Your health goals should account for your individual needs rather than focusing only on a BMI number.
Frequently Asked Questions About BMI
For standard adult BMI categories, a BMI between 18.5 and less than 25 is classified as healthy weight. However, BMI is only a screening measure and should not be considered a complete assessment of individual health.
Convert your weight to kilograms and your height to meters. Then divide your weight by your height squared.
BMI = Weight (kg) ÷ Height² (m)
For example, a person weighing 70 kg and measuring 1.75 m has a BMI of approximately 22.9.
No. BMI uses your height and weight to estimate weight status. It does not directly measure body fat or body composition.
Yes. Because BMI does not distinguish muscle from fat, people with high muscle mass may have a higher BMI even when they have relatively low body fat.
The standard adult BMI categories are generally the same for men and women. However, BMI does not account for individual differences in muscle mass or body composition.
