Sprint 7 Health Hub
BMI (Body Mass Index) Calculator
WHO-style BMI estimate from weight and height.
BMI
22.86
Category
Normal
How it works
Body Mass Index (BMI) is a numerical value derived from height and weight that places adults in one of four standard weight categories. The BMI Calculator computes your BMI instantly from metric (kg/cm) or imperial (lb/in) inputs and provides the category, health context, and the limitations you need to interpret the result intelligently.
BMI formula: - Metric: BMI = weight (kg) ÷ height (m)² - Imperial: BMI = (weight (lb) ÷ height (in)²) × 703
Standard WHO categories for adults (18+): - Under 18.5: Underweight - 18.5–24.9: Normal weight - 25.0–29.9: Overweight - 30.0 and above: Obese (Class I: 30–34.9, Class II: 35–39.9, Class III: 40+)
For children and teenagers, BMI is interpreted differently using age- and sex-specific percentile charts — this calculator is designed for adults.
Why BMI is useful but limited: BMI is a population-level screening tool, not a diagnostic measure. It correlates reasonably well with body fat percentage at the population level but fails for individuals in several known cases: - Athletes and people with high muscle mass: muscle weighs more than fat, so muscular individuals are often classified as overweight or obese despite having low body fat - Older adults: BMI may underestimate health risk as muscle mass decreases with age - Different ethnic groups: research shows Asian populations have higher health risk at lower BMI thresholds; some guidelines use 23.0 as the overweight threshold for Asian adults - Tall individuals: BMI slightly overestimates health risk for very tall people
Better complementary metrics: waist circumference (above 88cm/35in for women and 102cm/40in for men indicates elevated cardiovascular risk), waist-to-height ratio (under 0.5 is healthy), and body fat percentage measured by DEXA scan or bioelectrical impedance.
Privacy: all calculations run in the browser. No health data is transmitted.
Frequently Asked Questions
- The World Health Organization defines a BMI of 18.5–24.9 as 'normal weight' for adults 18 and older. BMI below 18.5 is classified as underweight; 25.0–29.9 as overweight; 30.0 and above as obese. However, these cutoffs are population-level guidelines with significant individual exceptions — athletes and muscular individuals often have 'overweight' BMIs with low body fat, while older adults and people with low muscle mass can have 'normal' BMIs with high body fat percentages.
- No. BMI cannot distinguish between fat mass and lean mass. A 180cm rugby player weighing 100kg has a BMI of 30.9 (obese) but may have only 12% body fat. Conversely, a sedentary person with a 'normal' BMI of 22 could have 30% body fat — a condition called 'normal weight obesity'. For people who exercise regularly, body fat percentage (measured by DEXA scan, bioelectrical impedance, or Navy circumference method) is a more meaningful health metric than BMI.
- No. Research consistently shows that people of South Asian, East Asian, and Southeast Asian descent have higher cardiometabolic risk at lower BMI values compared to people of European descent. The WHO consultation on BMI for Asian populations recommends using 23.0 as the overweight threshold and 27.5 as the obese threshold for East and South Asian populations, compared to 25.0 and 30.0 for the international standard. Some health organisations in Singapore, Japan, and India use these adjusted thresholds in clinical practice.
- BMI is a screening snapshot, not a dynamic health monitoring tool — checking it more than once every few months provides little additional information since significant weight changes take time. More useful for ongoing monitoring: waist circumference (monthly), body fat percentage (quarterly if you have access to measurement tools), and fitness metrics like resting heart rate and exercise performance (weekly or monthly). Focus on trends over time rather than point-in-time BMI values.