What is BMI?
BMI (Body Mass Index) is a simple screening measure that estimates whether an adult’s weight is appropriate for their height. It is widely used to group results into underweight, healthy weight, overweight, and obesity categories.
Adult BMI Calculator
Enter your height and weight to get an instant BMI result, adult weight category, and a practical healthy-weight reference for your height.
Enter your details
Choose your preferred units and provide your height and weight.
About this calculator
How to use this tool, plus the formulas and logic behind the results.
Tool description
The Adult BMI Calculator estimates body mass index from height and weight and shows the corresponding adult BMI category and a healthy weight range.
How to use
- Choose metric or US units.
- Enter your height and weight.
- Select Calculate BMI to view BMI, category, and healthy weight range.
- Use the reference table below to interpret common BMI ranges.
Formulas & reference
Metric: BMI = weight(kg) ÷ [height(m)]²US: BMI = 703 × weight(lb) ÷ [height(in)]²Healthy weight range uses BMI 18.5–24.9 for the entered height
Calculation logic
Height and weight are converted to metric when needed, then BMI is calculated and classified with standard adult cutoffs. BMI is a screening estimate, not a complete health assessment.
BMI FAQ
Common questions about body mass index, how it is calculated, and what the results mean.
How is BMI calculated?
In metric units, BMI = weight (kg) ÷ [height (m)]². In US units, BMI = 703 × weight (lb) ÷ [height (in)]². This calculator uses those standard formulas based on the unit system you select.
Is BMI accurate?
BMI is useful as a population-level screening tool, but it is not a perfect measure of individual health. It does not directly measure body fat, muscle mass, bone density, or fat distribution, so it should be interpreted alongside other health indicators.
What are the limitations of BMI?
BMI cannot distinguish between fat and muscle, and it does not account for waist circumference, fitness level, or medical history. Results may be less meaningful for athletes, pregnant people, older adults, growing children, and some ethnic groups.
Does BMI work for athletes?
Not always. Athletes and people with high muscle mass may have a higher BMI even when their body fat is low. In those cases, body fat percentage, waist measurements, and performance markers can be more informative than BMI alone.
Does BMI consider age?
Standard adult BMI categories do not adjust for age. Age-specific charts are used for children and teens. For older adults, BMI can still be useful, but muscle loss and other age-related changes mean additional assessments are often recommended.
Does BMI consider gender?
The adult BMI formula and category cutoffs are the same for men and women. However, typical body fat patterns can differ by gender, so clinicians may also look at waist circumference, body composition, and other risk factors.
What is a normal BMI?
For most adults, a BMI between 18.5 and 24.9 is considered a healthy or “normal-weight range. A result below 18.5 is usually classified as underweight, and 25.0 or higher falls into overweight or obesity categories.
What BMI is considered obese?
For adults, a BMI of 30.0 or higher is generally classified as obesity. Values from 25.0 to 29.9 are typically considered overweight. These cutoffs are screening guidelines and not a medical diagnosis on their own.
Can BMI predict health?
BMI can help flag potential weight-related health risks at a group level, but it cannot predict an individual’s health by itself. Blood pressure, cholesterol, blood sugar, activity level, diet, and family history all matter as well.
BMI vs Body Fat
BMI estimates weight relative to height, while body fat percentage estimates how much of your body is fat tissue. Someone can have a high BMI with low body fat (common in muscular people), or a "normal" BMI with higher body fat. Body composition tests give a clearer picture of fat versus lean mass.