BMI Calculator — Calculate Your Body Mass Index Instantly
Your weight alone tells you very little. A 90 kg person who is 6'2" is in a completely different health category than a 90 kg person who is 5'4". That's exactly why body mass index exists — and why a reliable BMI converter matters more than stepping on a scale.
Calculate your Body Mass Index (BMI) instantly using metric or imperial units, standard WHO guidelines, formulas, and growth percentiles. Understand your weight category relative to height and explore its medical significance. Assess whether your weight falls into a healthy, underweight, overweight, or obese classification.
How to Use the bmi
Body Mass Index is a numerical value calculated from a person's height and weight. It is a fast, cost-free screening tool to categorize body weight and correlate health risks across large populations.
- 1Select your preferred units (metric or imperial).
- 2Enter your weight in kilograms or pounds in the first field.
- 3Enter your height in centimeters or feet/inches, and click calculate to view your score.
The Standard BMI Formula
The BMI calculation divides weight in kilograms by the square of height in meters. For imperial units, the result is multiplied by a scaling factor of 703 to match the metric scale.
Metric: BMI = weight (kg) ÷ height² (m²)
Imperial: BMI = (weight (lbs) × 703) ÷ height² (inches²)Common Reference Values & Comparisons
Refer to this table to study common calculations, reference ratios, or performance profiles for this tool:
| BMI Score Range | WHO Weight Classification |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Normal weight |
| 25.0 – 29.9 | Overweight |
| 30.0 – 34.9 | Obesity Class I |
| 35.0 – 39.9 | Obesity Class II |
| 40.0 and above | Severe Obesity Class III |
| 10th Percentile (Child) | Healthy Weight |
| 90th Percentile (Child) | Overweight |
| 98th Percentile (Child) | Obese |
| Average Global BMI | 23.5 (Normal) |
Frequently Asked Questions (FAQ)
Not equally. BMI is a population-level screening tool. It works reasonably well across large groups but can misclassify individuals — particularly highly muscular people, older adults with low muscle mass, and certain ethnic populations.
Yes. Body composition shifts with age — muscle mass often decreases while fat mass can increase, even at stable weight. This means your health risk profile can change even if your BMI stays the same.
The standard WHO ranges apply to both sexes. However, women naturally carry a higher percentage of body fat than men at equivalent BMI values, which some researchers argue warrants sex-specific interpretation.
For most healthy adults, checking every few months during a fitness or wellness program is reasonable. Annual checks are sufficient for general health monitoring.
Yes, in many countries. Insurers often use BMI alongside other health indicators to assess risk and set premium levels.
While BMI is an excellent starting point, it is not a diagnostic tool. If your BMI falls outside the normal range, it represents an invitation to discuss your overall wellness with a certified medical provider rather than a definitive diagnosis of health.
Related Tools