Body Mass Index (BMI)

Q: What is BMI?

BMI is a screening tool that estimates body fat using height and weight.

Q: Can BMI diagnose obesity?

No. BMI is only a screening tool and should always be interpreted together with clinical findings.

Calculates Body Mass Index.

Anthropometry General MedicineEvidence-BasedUpdated 2026-08-06

Clinical Notes

Formula

weight / (height * height)

Normal Range

18.5–24.9 kg/m²

Clinical Notes

Interpret results together with the patient's clinical presentation.

References

MedCalcHub Clinical References

Calculator Information

Specialty

General Medicine

📋 Reference Ranges

Normal Range

18.5–24.9 kg/m²

Reference ranges for this calculator
Classification	Range
Underweight	<18.5
Normal weight	18.5–24.9
Overweight	25–29.9
Obesity	≥30

What This Calculator Measures

Calculates Body Mass Index (BMI) to screen for underweight, normal weight, overweight, and obesity categories.

How to Use

Enter the patient's weight in kilograms.
Enter the patient's height in centimeters.
Review the BMI value and weight category.

Interpretation Guide

BMI <18.5 is underweight. 18.5–24.9 is normal weight. 25–29.9 is overweight. ≥30 is obesity.

Pediatric ranges differ

Clinical Significance

BMI is a widely used screening tool that correlates with metabolic risk. While not a perfect measure of body fatness, it provides a quick, inexpensive assessment that guides further clinical evaluation and intervention.

When to Use

Initial screening for weight status in adults
Population-level health assessments
Baseline measurement for weight management programs
Cardiovascular and metabolic risk assessment

When Not to Use

As a sole diagnostic criterion for obesity in athletes or individuals with high muscle mass
In very elderly patients where body composition changes may affect interpretation
As a replacement for more detailed body composition analysis when clinically needed

Limitations

Does not distinguish between fat mass and lean mass.
May misclassify muscular individuals as overweight or obese.
Less accurate in elderly patients, athletes, and pregnant women.
Does not account for fat distribution (use waist-to-hip ratio for central obesity assessment).
Pediatric BMI interpretation requires age- and sex-specific percentiles.

Worked Example

A 35-year-old woman weighs 68 kg and is 165 cm tall.

Inputs:

weight: 68

height: 165

BMI = 68 / (1.65)² = 24.98 kg/m². This is at the upper end of normal weight, bordering on overweight.

Evidence

Source: Anthropometry / WHO
Reference: WHO. Body Mass Index — BMI. World Health Organization.
Reviewed By: MedCalcHub Clinical Team
Version: 2000
Updated: 2026-08

WHO. Body Mass Index — BMI.

References

WHO. Body Mass Index — BMI. World Health Organization. (Guideline)

Frequently Asked Questions

What is BMI?

BMI is a screening tool that estimates body fat using height and weight.

Can BMI diagnose obesity?

No. BMI is only a screening tool and should always be interpreted together with clinical findings.

Disclaimer: This calculator is intended for educational and clinical screening purposes only. BMI is a screening tool and does not diagnose body fatness or health. Clinical decisions should be based on comprehensive patient assessment.

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