What is BMI?
Body Mass Index (BMI) is a measure derived from a person’s weight and height. It provides a simple numeric measure of body fatness for adults, helping identify potential health risks related to underweight, overweight, or obesity.
How is BMI Calculated?
The BMI formula is straightforward:
BMI = Weight (kg) ÷ Height² (m²)
For example, if you weigh 70 kg and are 1.75 m tall:
BMI = 70 ÷ (1.75 × 1.75) = 70 ÷ 3.0625 = 22.9
BMI Categories (WHO Guidelines)
- Below 18.5 — Underweight
- 18.5 – 24.9 — Normal weight (healthy)
- 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 (morbid)
Limitations of BMI
While BMI is a useful screening tool, it has limitations:
- It does not distinguish between fat and muscle mass
- Athletes with high muscle mass may show a high BMI despite being healthy
- It does not account for fat distribution (belly fat vs. overall fat)
- BMI ranges may differ for different ethnic groups
BMI for Children and Teenagers
For children and teens aged 2–19, BMI is interpreted differently using age- and sex-specific percentile charts from the CDC, since body composition changes with age.
Calculate Your BMI Free
Use our free BMI calculator to instantly find your BMI in metric or imperial units. No registration required — get your results in seconds.
What to Do After Knowing Your BMI
- Consult your doctor for a personalized health assessment
- Consider waist circumference as an additional metric
- Focus on lifestyle changes: balanced diet and regular exercise
- Use our calorie calculator to plan your nutrition
