BMI Calculator
Standard BMI, Trefethen New BMI, WHtR, and BRI in one tool.
100% in your browser — nothing uploadedCalculate BMI, New BMI, waist-to-height ratio, and body roundness index
Decimals: use a period or a comma — 99.5 or 99,5.
Note: WHO recommends lower thresholds for Asian populations — overweight ≥ 23, obese ≥ 27.5.
BMI is a screening tool, not a diagnosis. It does not account for muscle mass, bone density, age, sex, or ethnicity. Consult a healthcare professional for personalized advice.
About this BMI calculator
Enter your height and weight to get your body mass index calculated four different ways. The standard BMI (weight / height²) is the WHO baseline. The Trefethen New BMI (1.3 × weight / height^2.5), proposed by Oxford mathematician Nick Trefethen in 2013, corrects for the well-known bias that makes tall people appear heavier and short people lighter than they are.
Optionally enter your waist circumference to unlock two more metrics. The waist-to-height ratio (WHtR) is a simple but powerful predictor of cardiometabolic risk — the guideline is to keep your waist below half your height. The body roundness index (BRI) uses an eccentricity-based formula to estimate body shape roundness, correlating with visceral fat and health risk.
Both metric (kg/cm) and imperial (lb/ft+in) units are supported. The calculator converts everything to metric internally and shows all four metrics side by side. WHO BMI categories are color-coded from blue (underweight) through green (normal) and amber (overweight) to red (obese classes I–III). When the BMI falls in the 23–30 range, a note reminds you that WHO recommends lower thresholds for Asian populations.
BMI is a screening tool, not a diagnosis. It does not account for muscle mass, bone density, age, sex, or ethnicity. Athletes and bodybuilders routinely score "overweight" or "obese" on BMI despite low body fat. That is exactly why this tool shows multiple metrics — the WHtR and BRI provide a more complete picture when waist data is available. For personalized health advice, consult a healthcare professional.
FAQ
What is the Trefethen New BMI?
A 2013 formula by Oxford's Nick Trefethen that uses height^2.5 instead of height² to correct the standard BMI's bias toward tall and short people. It gives more accurate results at height extremes while matching standard BMI near average height.
What is a healthy waist-to-height ratio?
Below 0.5 is generally considered healthy — meaning your waist should be less than half your height. Above 0.5 is associated with increased cardiometabolic risk regardless of BMI.
Is my health data private?
Yes. All calculations run locally in your browser. No health data — height, weight, waist — is sent to any server or stored anywhere.