Body Mass Index (BMI) is a measurement that helps you understand whether your weight is healthy for your height. It’s one of the most commonly used tools by healthcare providers and individuals to screen for possible weight-related health issues because it’s quick and straightforward.
Our BMI calculator uses a standard formula based on your height and weight to give you a BMI value that falls into one of the main weight categories — underweight, healthy weight, overweight, or obese. By entering your height and weight in either metric (kg/m) or imperial (lb/in) units, you can get your result instantly and see where you stand.
How BMI Is Calculated
Your BMI is calculated by dividing your weight by the square of your height:
- Metric system: BMI = weight (kg) ÷ [height (m)]²
- Imperial system: BMI = [weight (lbs) ÷ height (in)²] × 703
This gives you a value expressed in kg/m², which is then interpreted using standard health risk categories.
Body Mass Index Calculator
BMI Categories & What They Mean
After calculating your BMI, your result will place you into one of the following widely accepted categories:
- Underweight: less than 18.5
- Healthy Weight: 18.5 – 24.9
- Overweight: 25 – 29.9
- Obese: 30 or more
These categories help indicate whether your weight might be associated with increased risk for conditions like type 2 diabetes, heart disease, and other long-term health issues — though BMI is just one part of the overall picture.
Why This BMI Calculator Is for Adults Only
Our BMI calculator is designed for adults aged 18 and over. The reason people under 18 shouldn’t use this adult calculator is because body composition and growth patterns in children and teenagers are different from adults. Younger people are still growing, and their proportions and fat distribution change with age and sex — so adult BMI categories simply don’t apply in the same way.
For example, children’s BMI results are interpreted using percentile charts that compare a child’s BMI with others of the same age and sex. This method recognizes normal growth and development patterns as kids grow taller and heavier at different stages — something a standard adult BMI number can’t properly account for.
If you’re under 18, please use a children’s or teenager BMI calculator that takes age and sex into account rather than this adult BMI tool.
Important to Know: BMI’s Limitations
While BMI is a useful general screening tool, it doesn’t measure body fat directly and doesn’t account for differences in muscle mass, bone density, sex, or ethnicity. For example:
- A muscular athlete might have a higher BMI even with low body fat.
- Older adults and people from certain ethnic backgrounds may have different health risks at the same BMI values.
That’s why BMI should be used as a guide — not a diagnosis — and ideally considered alongside other measures like waist circumference, physical activity, and overall health assessments.
How to Use This Calculator
- Enter your height and weight in the fields above.
- Choose your measurement units (metric or imperial).
- Click Calculate to get your BMI result and weight category.
- Use this result to better understand your health and, if needed, discuss it with a healthcare professional.
In Summary
The BMI calculator provides:
A fast, reliable way to estimate whether your weight is healthy for your height
A clear BMI category based on globally recognized standards
A starting point for weight and health discussions with professionals
—but it is not suitable for people under 18 and should not replace professional medical advice.