BMI Calculator
Body Mass Index
How to Calculate BMI Manually
Understanding how BMI is calculated helps you better interpret your results. Learn both metric and imperial formulas. Use our BMI Calculator to calculate your BMI automatically, or check the BMI Chart to see where your BMI falls.
Metric BMI Formula
or more precisely:
Example Calculation
Person: 70 kg, 1.75 m tall
BMI = 70 ÷ (1.75 × 1.75)
BMI = 70 ÷ 3.0625
BMI = 22.86 (Normal weight) (Normal weight)
Imperial BMI Formula
Example Calculation
Person: 154 lbs, 68 inches tall
BMI = (154 × 703) ÷ (68 × 68)
BMI = 108,262 ÷ 4,624
BMI = 23.41 (Normal weight) (Normal weight)
Why This Formula Works
The BMI formula was developed in the 19th century by Adolphe Quetelet, a Belgian mathematician, sociologist, and statistician. It was originally called the "Quetelet Index."
The formula creates a relationship between height and weight that correlates reasonably well with body fat percentage for most people. The squaring of height in the denominator accounts for the fact that weight increases with the cube of linear dimensions, while height is only linear. Learn more about what constitutes a healthy BMI.
The constant 703 in the imperial formula is a conversion factor that makes the imperial calculation equivalent to the metric version.
Formula Limitations
- BMI doesn't distinguish between muscle and fat
- Athletes may be classified as "overweight" despite being healthy
- Doesn't account for age, gender, or ethnicity differences
- May not be accurate for very tall or short individuals
- Not suitable for children under 20 or pregnant women
Medical Disclaimer
Important: BMI is a screening tool, not a diagnostic tool. It provides an estimate of body fat based on height and weight but does not directly measure body fat percentage, muscle mass, bone density, or overall health.
BMI should not be used as the sole indicator of health. Many factors influence health beyond BMI, including:
- Body composition (muscle vs. fat)
- Waist circumference and body fat distribution
- Physical fitness and activity levels
- Medical history and family history
- Blood pressure, cholesterol, and blood sugar levels
- Lifestyle factors (diet, exercise, sleep, stress)
This calculator provides educational information only and is not a substitute for professional medical advice, diagnosis, or treatment. Always consult with a qualified healthcare provider for personalized health guidance, especially if you have concerns about your weight or health status.