BMI Calculator: Calculate Your Body Mass Index
Body Mass Index (BMI) is a widely used screening tool that estimates body fat based on height and weight. Our free BMI Calculator supports both metric and imperial units and shows your BMI category, a visual scale, and your healthy weight range.
How to Use the Calculator
- Choose your unit system: Metric (kg/cm) or Imperial (lb/ft/in)
- Enter your weight: In kilograms or pounds
- Enter your height: In centimeters, or feet and inches
- Click Calculate: See your BMI value, category, and healthy weight range
Understanding BMI Categories
| BMI Range | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 - 24.9 | Normal weight |
| 25.0 - 29.9 | Overweight |
| 30.0 - 34.9 | Obese (Class I) |
| 35.0 - 39.9 | Obese (Class II) |
| 40.0 and above | Obese (Class III) |
The BMI Formula
Metric: BMI = weight (kg) / height (m)^2
Imperial: BMI = 703 x weight (lb) / height (in)^2
For example, a person weighing 70 kg at 175 cm tall: BMI = 70 / (1.75)^2 = 22.9 (Normal weight).
What BMI Tells You
BMI is a screening tool, not a diagnosis. It provides a quick estimate of whether your weight is in a healthy range for your height. The visual scale on the calculator shows where your BMI falls relative to the standard categories.
The calculator also shows your healthy weight range — the weight range that corresponds to a BMI of 18.5-24.9 for your height.
Limitations of BMI
BMI does not account for:
- Muscle mass: Athletes may have a high BMI due to muscle, not fat
- Body composition: Two people with the same BMI can have very different body fat percentages
- Age and sex: BMI ranges don’t adjust for age or sex differences
- Bone density: People with denser bones may weigh more
- Distribution of fat: Where fat is stored matters for health risk
Tips
- Use BMI as one data point, not the only measure of health
- Track BMI over time to see trends rather than focusing on a single reading
- For a more complete picture, combine BMI with waist circumference and body fat percentage
- Consult a healthcare professional for personalized health assessment
Frequently Asked Questions
Is BMI accurate for children? This calculator is for adults (18+). Children’s BMI is calculated differently, using age and sex-specific percentiles.
Does BMI apply to pregnant women? BMI during pregnancy is not meaningful for the same categories. Pre-pregnancy BMI is used for clinical guidance.
Why does my doctor still use BMI? Despite its limitations, BMI is a quick, free screening tool that correlates with health risks at the population level.
Try our free BMI Calculator to check your Body Mass Index.
