BMI CALCULATOR
Precision Body Mass Index analysis using WHO adult standards. Metric and Imperial units. Runs entirely in your browser — no data stored.
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Your BMI Score
00.0
BMI is a screening tool. Consult a healthcare professional for medical advice.
Transparency & Logic
Calculation Formula
Metric: BMI = weight(kg) ÷ height(m)²
Imperial: BMI = (weight(lbs) ÷ height(in)²) × 703WHO Adult Classification
Understanding Your BMI
Body Mass Index (BMI) is a widely used screening tool to identify possible weight-related health concerns in adults. Developed from population studies, it provides a simple numeric measure from your height and weight alone.
Why we ask for age and gender
The core WHO formula applies universally across age and gender for adults. However, body composition varies — women typically carry proportionally more body fat than men at the same BMI, and older adults tend toward higher fat ratios. We collect this context to provide more relevant result information, while the underlying calculation remains the universal WHO standard.
Clinical Limitations of BMI
BMI is a population-level screening indicator, not a clinical diagnosis. It does not directly measure body fat, account for muscle mass distribution, bone density, ethnicity-specific differences, or pregnancy.
Athletes and highly muscular individuals frequently register BMI values in the "Overweight" or "Obese" range despite having low body fat. Conversely, some individuals with a "Normal" BMI may carry clinically high body fat levels.
This tool is intended for adults (18+). For children aged 2–17, consult a paediatric BMI calculator which accounts age and gender-adjusted CDC percentile charts.
How to Improve Your BMI
Balanced Nutrition
Focus on whole foods, lean proteins, vegetables, and complex carbohydrates. A registered dietitian can create a plan suited to your specific health profile and goals.
Regular Physical Activity
The WHO recommends at least 150–300 minutes of moderate-intensity aerobic activity per week for adults, combined with muscle-strengthening activities on 2 or more days.
Professional Guidance
Always consult a qualified healthcare professional — doctor, dietitian, or physiotherapist — before beginning any weight management programme, particularly if you have existing health conditions.
BMI by Age and Gender
BMI for Women vs. Men
The standard WHO BMI formula applies identically to both men and women. However, the interpretation differs. At an identical BMI value, women typically carry 10–12% more body fat than men due to physiological differences — reproductive hormones, breast tissue, and the needs of childbearing.
This means a woman with a BMI of 24 and a man with a BMI of 24 have the same calculation result, but the woman will generally have a higher body fat percentage. This is entirely normal and expected. The WHO thresholds remain the same across genders for clinical screening purposes.
How BMI Changes with Age
As adults age, body composition shifts even when weight remains constant. Muscle mass typically declines after age 30 (a process called sarcopenia), while body fat tends to increase. This means older adults may have a "Normal" BMI while carrying proportionally more fat than their younger counterparts.
For adults over 65, some research suggests that a slightly higher BMI (up to 27) may actually be associated with better health outcomes — a phenomenon known as the "obesity paradox." This is why BMI must always be evaluated alongside other clinical markers, never in isolation.
Ethnicity and BMI: What the Research Shows
Standard WHO BMI thresholds were largely derived from studies of European populations. Research published in the Lancet and adopted by several national health bodies suggests that people of Asian descent may experience metabolic risks at lower BMI values — around 23 for overweight rather than the standard 25.
Conversely, some studies indicate that people of African and Pacific Islander descent may have lower associated health risks at higher BMI values. The World Health Organisation continues to review ethnic-specific cut-off points. Our calculator uses the universal WHO adult thresholds — always discuss your result with a healthcare professional familiar with your background.
Metric vs. Imperial BMI — What's the Difference?
Our calculator supports both the Metric system (kilograms and centimetres, standard in most of the world) and the Imperial system (pounds, feet, and inches, commonly used in the United States and UK). The resulting BMI score is mathematically identical regardless of which system you use.
Metric (kg / cm)
Enter your weight in kilograms (kg) and height in centimetres (cm). The formula divides your weight by your height in metres squared.
Example: 70 kg, 175 cm
BMI = 70 ÷ (1.75 × 1.75) = 22.9Imperial (lbs / ft / in)
Enter your weight in pounds (lbs) and height in feet and inches. The formula uses a conversion factor of 703.
Example: 154 lbs, 5 ft 9 in (69 in)
BMI = (154 ÷ 69²) × 703 = 22.7Both calculations produce the same BMI result (minor rounding differences aside). Choose whichever unit system you're most comfortable with — switching between Metric and Imperial in our calculator resets the inputs and relabels the fields automatically.