BMI Calculator
Calculate BMI from height and weight in a few seconds and use the result as a screening metric, not a full health diagnosis.
How to use this BMI calculator
- Enter height
Enter your height in the height field.
- Enter weight
Enter your body weight in the weight field.
- Choose unit system
Select metric (kg, cm) or imperial (lb, in) to match your measurements.
- Review results
Check your BMI value and the corresponding category (underweight, normal, overweight, or obese).
How this BMI calculator works
This BMI calculator estimates body mass index from your height and weight, then compares the result with the standard adult BMI category ranges. It is useful as a quick screening tool when you want a simple height-to-weight ratio, but it should not be treated as a direct measurement of body fat or a complete picture of health.
BMI = (weight (lb) / height (in)^2) * 703 BMI = (weight (lb) / height (in)²) × 703 A person who weighs 75 kg and is 180 cm tall has a BMI of roughly 23.1. That falls inside the commonly cited adult 'normal weight' range, but the number still does not capture training status, age, or body composition differences.
A person who weighs 165 lb and is 70 in tall has a BMI of roughly 23.7. That falls inside the commonly cited adult 'normal weight' range, but the number still does not capture training status, age, or body composition differences.
A person who weighs 52 kg and is 175 cm tall has a BMI of roughly 17.0, which falls inside the underweight range. A low BMI can sometimes signal insufficient calorie intake or an underlying health condition, so it is worth discussing with a healthcare provider, especially if unintentional weight loss is involved.
A person who weighs 95 kg and is 170 cm tall has a BMI of roughly 32.9, which falls inside the obese class I range. A BMI in this range is associated with elevated risk for conditions such as type 2 diabetes, cardiovascular disease, and joint stress, but it is only one data point and should be interpreted alongside waist circumference, blood work, and overall fitness level.
- ✓ The estimate uses the standard adult BMI formula based only on height and weight.
- ✓ BMI is a screening measure and does not directly account for muscle mass, body composition, or fat distribution.
- ✓ The result is most useful as a starting point for context, not a medical diagnosis.
- BMI can be less informative for athletes, older adults, and anyone whose body composition differs significantly from the average assumptions behind the measure.
- If the result raises concerns, it is best used alongside waist measurements, medical guidance, and a broader review of health markers.
- Quetelet's body mass index — Keys, A. et al., 'Indices of Relative Weight and Obesity,' Journal of Chronic Diseases, 1972
- WHO Expert Consultation, 'Appropriate BMI for Asian Populations,' The Lancet, 2004
- CDC Adult BMI Classification — Centers for Disease Control and Prevention
What is BMI?
Body mass index is a simple numerical ratio derived by dividing a person's weight in kilograms by the square of their height in metres. Belgian mathematician Adolphe Quetelet originally developed the formula in the early 19th century as a population-level statistic, not an individual diagnostic tool. Despite that origin, BMI became widely adopted in clinical and public-health settings because it requires only two easily obtained measurements and produces a single number that can be compared across large groups. The index does not distinguish between fat mass and lean mass, so two people with identical BMIs can have very different body compositions. Still, at the population level it correlates reasonably well with body-fat percentage and with the prevalence of weight-related health conditions, which is why organisations such as the WHO and the CDC continue to use it as a first-pass screening metric.
BMI categories and what they mean
The standard adult BMI categories divide the continuous scale into four broad ranges. A BMI below 18.5 is classified as underweight and may indicate nutritional deficiency, low muscle mass, or other health concerns. The 18.5 to 24.9 range is labelled normal weight and is generally associated with the lowest statistical risk for weight-related chronic diseases. A BMI of 25.0 to 29.9 is categorised as overweight, and values of 30.0 and above fall into the obese range, which is sometimes subdivided into class I (30.0 to 34.9), class II (35.0 to 39.9), and class III (40.0 and above). Each step up the scale is associated with progressively higher population-level risk for conditions like type 2 diabetes, hypertension, sleep apnoea, and certain cancers. However, individual risk depends on many factors beyond a single number, including fitness level, fat distribution, genetics, and metabolic markers.
Limitations of BMI
BMI has well-documented blind spots. Because it relies solely on height and weight, it cannot differentiate muscle from fat. A lean, muscular athlete may register an overweight or obese BMI despite having low body-fat levels, while a sedentary person with low muscle mass but high visceral fat could show a normal BMI. The formula also does not account for bone density, frame size, age-related changes in body composition, or sex-based differences in fat storage patterns. Ethnic variation adds another layer: research shows that some Asian populations face higher metabolic risk at lower BMI thresholds, prompting regional adjustments. For these reasons, clinicians increasingly use BMI alongside waist circumference, waist-to-hip ratio, blood pressure, blood lipid panels, and functional fitness assessments to form a more complete picture of an individual's health status.
BMI calculator FAQs
What does BMI stand for?
BMI stands for body mass index, a screening measure that compares weight with height.
What are the common adult BMI categories?
Standard adult ranges commonly group BMI below 18.5 as underweight, 18.5 to 24.9 as normal weight, 25.0 to 29.9 as overweight, and 30 or higher as obesity.
Is BMI accurate for athletes?
Not always. Athletes or muscular individuals can have a higher BMI because of lean mass rather than excess body fat.
Does BMI measure body fat directly?
No. BMI is only a height-to-weight ratio, so it cannot directly measure body fat percentage.
Why can two people with the same BMI look very different?
Because BMI does not capture body composition, one person can carry more muscle while another carries more fat even if their BMI matches.