What is the BMI formula?
BMI = weight (kg) ÷ [height (m)]². For imperial units: BMI = (weight ÷ height²) × 703.
BMI Formula – How to Calculate Body Mass Index
Body Mass Index (BMI) is calculated using a simple formula that relates weight to height. This page explains the formula, variations for adults and children, and provides practical examples for easy understanding.
BMI Calculator to instantly calculate your BMI using this formula and get your health category.
Standard BMI Formula for Adults
- BMI = weight (kg) ÷ [height (m)]²
- For weight in pounds and height in inches: BMI = (weight ÷ height²) × 703
- BMI provides an estimate of body fat and is used as a screening tool for health risks.
BMI Formula for Children
BMI for children uses the same calculation as adults (weight ÷ height²) but is interpreted using age- and gender-specific percentile charts.
- Percentiles indicate how a child's BMI compares to peers of the same age and gender.
BMI Prime – Optional Calculation
- BMI Prime = BMI ÷ Upper Healthy BMI Limit (usually 25)
- A BMI Prime of 1.0 means you are at the upper limit of a healthy BMI; values above 1 indicate overweight risk.
Examples of BMI Calculation
Adult Example
- Weight: 70 kg, Height: 1.75 m → BMI = 70 ÷ (1.75)² = 22.9 → Normal
Child Example
- Weight: 32 kg, Height: 1.4 m → BMI = 32 ÷ (1.4)² = 16.3 → Check percentile chart → Healthy
Using BMI Prime
- Adult BMI = 30, Upper Healthy BMI = 25 → BMI Prime = 30 ÷ 25 = 1.2 → Overweight risk
Tips for Accurate Calculation
- Measure height without shoes and weight in light clothing.
- Use metric units or convert correctly from imperial units.
- Recheck periodically to monitor trends rather than relying on a single value.
BMI Formula FAQ
Is the BMI formula the same for children?
Yes, the calculation is the same but results are interpreted using age- and gender-specific percentiles.
What is BMI Prime?
BMI Prime compares BMI to the upper healthy limit (usually 25) to assess overweight risk.
Can I use BMI formula for athletes?
Yes, but interpret with caution as higher muscle mass can inflate BMI without increasing fat.
Medical References & Trusted Sources
- World Health Organization (WHO) - Global authority on obesity classification and health standards. Our BMI categories follow WHO guidelines established in 1993.
- Centers for Disease Control and Prevention (CDC) - Leading U.S. public health agency providing evidence-based guidelines for weight assessment and health promotion.
- National Institutes of Health (NIH) - Primary U.S. agency for biomedical research, providing comprehensive health information and clinical guidelines.
- Mayo Clinic - World-renowned medical institution providing patient-centered health information and evidence-based medical guidance.