What is BMI (Body Mass Index)?
BMI is a simple index that estimates body fat level from height and weight. The formula is weight (kg) Γ· height (m)Β², and this calculator uses the World Health Organization (WHO) international classification.
Weight categories (WHO classification)
- Below 18.5: Underweight
- 18.5 β 24.9: Normal weight
- 25 β 29.9: Overweight
- 30 and above: Obese
Example calculation
For someone 5'7" (170 cm) and 143 lb (65 kg): 65 Γ· (1.7 Γ 1.7) = 22.5 β within the normal weight range.
A note on accuracy
BMI is a simple screening tool based only on height and weight β it does not account for muscle mass, body fat percentage, age, sex, or ethnicity. Many national health authorities (for example, several Asia-Pacific guidelines) use somewhat lower BMI cutoffs than the WHO international standard shown here, so treat this result as general information rather than a medical diagnosis. If you have health concerns related to weight, consult a doctor or dietitian.
Frequently Asked Questions
Can my BMI be normal even if my body fat percentage is high?
Yes. BMI doesn't distinguish between muscle and fat, so someone with a lot of muscle mass can have a high BMI with a low body fat percentage. A body composition scan gives a more accurate picture.
How is the ideal weight calculated?
This calculator uses a BMI of 22 as the reference point for ideal weight. Ideal weight (kg) = 22 Γ height (m)Β².
Does this apply to children and teenagers?
This is an adult standard. For anyone under 18, growth-stage-specific pediatric growth charts (based on percentiles) should be used instead for an accurate assessment.