BMI Calculator
Calculate your Body Mass Index using the WHO standard classification. Supports metric and imperial units with full health risk interpretation and ideal weight range.
⚖️ Calculate Your BMI
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What Is BMI and How Is It Calculated?
Body Mass Index (BMI) is a numerical value derived from a person's weight and height. It is widely used as a screening tool to categorise individuals into weight status categories — underweight, normal weight, overweight, and obesity — as defined by the World Health Organization (WHO). For children and teens, see the pediatric tools in our Medical tools hub.
BMI Formula
The standard formula used by this calculator:
- Metric: BMI = weight (kg) ÷ height (m)²
- Imperial: BMI = 703 × weight (lb) ÷ height (in)²
WHO BMI Classification
- Below 18.5 — Underweight
- 18.5 – 24.9 — Normal weight (healthy range)
- 25.0 – 29.9 — Overweight
- 30.0 – 34.9 — Obesity Class I
- 35.0 – 39.9 — Obesity Class II
- 40.0 and above — Obesity Class III (severe)
Limitations of BMI
BMI is a useful population-level screening tool but has known limitations at the individual level. It does not account for muscle mass, bone density, fat distribution, age, or ethnicity. Athletes may be classified as overweight despite low body fat. For a more complete picture, use our body fat percentage calculator alongside your BMI. Older adults may carry excess fat at a normal BMI — pairing BMI with a waist-to-hip ratio check gives a more accurate cardiovascular risk picture.
Healthy Weight Range
This calculator shows your healthy weight range — the weight corresponding to a BMI of 18.5 to 24.9 for your height. To understand how many calories you need to reach or maintain that range, use our calorie calculator and basal metabolic rate (BMR) calculator. For fitness-specific weight goals, visit our Fitness & Wellness tools.
⚠️ This tool is for informational purposes only and does not constitute medical advice. Consult a qualified healthcare professional for clinical decisions.