BMI Calculator
Select your unit system, enter your details, and click calculate to get your Body Mass Index (BMI).
What is Body Mass Index (BMI)?
Body Mass Index (BMI) is a quick screening tool that estimates whether your weight is in a healthy range for your height. It does not directly measure body fat, but it is commonly used by doctors, fitness professionals, and public health organizations as a first check.
How do I calculate BMI?
Metric formula
If you use kilograms and meters:
BMI = weight (kg) ÷ [height (m)]²
Example: If your weight is 70 kg and your height is 1.75 m:
BMI = 70 ÷ (1.75 × 1.75) = 22.9
Imperial formula
If you use pounds and inches:
BMI = [weight (lb) ÷ height (in)²] × 703
Example: If your weight is 165 lb and height is 69 in:
BMI = (165 ÷ 69²) × 703 = 24.4
BMI categories for adults
| BMI Value | Weight Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 to 24.9 | Healthy weight |
| 25.0 to 29.9 | Overweight |
| 30.0 and above | Obesity |
Step-by-step guide to calculate BMI manually
- Measure your weight accurately (without heavy clothing if possible).
- Measure your height accurately.
- Use the metric or imperial formula shown above.
- Round your result to one decimal place.
- Compare your result with the BMI category chart.
Why BMI is useful
- Fast and easy to calculate
- Low-cost screening method
- Useful for tracking trends over time
- Helpful starting point for discussing health risks
Limitations of BMI
BMI is helpful, but it is not perfect. It does not account for muscle mass, body composition, bone density, sex differences, or fat distribution. For example, athletes may have a high BMI due to muscle, not excess body fat.
For a fuller picture of health, combine BMI with:
- Waist circumference
- Body fat percentage
- Blood pressure, blood sugar, and cholesterol checks
- Medical guidance from a healthcare professional
How often should I check BMI?
For most adults, checking once every few months is enough unless your doctor recommends closer monitoring. Use BMI trends over time rather than obsessing over one single number.
Final takeaway
If you are asking, “how do I calculate body mass index,” the process is straightforward: divide weight by height squared (using the correct formula for your units), then compare the result to standard categories. Use BMI as a practical screening tool, and pair it with other health indicators for better decision-making.