BMI Calculator
Calculate your Body Mass Index (BMI) in metric or imperial units and see your weight category instantly.
How to Use
- 1
Choose unit system
Select Metric (cm/kg) or Imperial (ft+in/lbs).
- 2
Enter height and weight
Fill in your height and weight.
- 3
View BMI
See your BMI value and weight category.
How It Works
Body Mass Index is a screening ratio of weight to height, used by health organizations worldwide as a quick population-level indicator — not a diagnostic measurement of body fat.
The formula
Metric: BMI = weight (kg) ÷ height (m)². Imperial: BMI = 703 × weight (lbs) ÷ height (in)². This tool converts imperial inputs to metric internally before calculating, so both unit systems return an identical BMI for the same body size.
Standard WHO categories
Below 18.5: Underweight. 18.5–24.9: Normal weight. 25.0–29.9: Overweight. 30.0 and above: Obese (often further split into Class I, II, III at 30, 35, and 40). These thresholds are the same ones used by the WHO and most national health services.
Examples
Metric example
Weight 70 kg, height 1.75 m: BMI = 70 ÷ (1.75 × 1.75) = 70 ÷ 3.0625 ≈ 22.9 — in the Normal range.
Imperial example
Weight 154 lbs, height 5'9" (69 in): BMI = 703 × 154 ÷ (69 × 69) = 108,262 ÷ 4,761 ≈ 22.7 — matches the metric result for the equivalent body size (70 kg / 175 cm), confirming the conversion is consistent.
Common Use Cases
- Quick self-check of weight category before consulting a doctor or nutritionist
- Tracking BMI trend over time alongside a weight-loss or fitness program
- Screening reference used by insurers, employers (for wellness programs), and clinics
Tips
- BMI doesn't distinguish muscle from fat — muscular athletes often show as "overweight" despite low body fat, because BMI can't tell the difference.
- It's less reliable for people over 65 (where some extra weight is protective), for children and teens (who need age/sex-specific percentile charts, not adult BMI bands), and during pregnancy.
- Use BMI as one data point alongside waist circumference, body fat %, and how you actually feel — not as a standalone health verdict.
Frequently Asked Questions
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