BMI Calculator
Calculate your Body Mass Index.
What is BMI?
Body Mass Index (BMI) is a simple screening metric calculated by dividing your weight in kilograms by your height in meters squared. The World Health Organization classifies BMI into categories: underweight (below 18.5), normal weight (18.5–24.9), overweight (25–29.9), and obese (30+). While BMI is a useful population-level indicator, it doesn't distinguish between muscle and fat mass, so athletes and older adults may get misleading results.
How to Use
- Select your preferred unit system (metric or imperial).
- Enter your height and weight accurately-small errors compound in the formula.
- Review your BMI value and category, keeping in mind that this is a screening tool, not a diagnosis.
Frequently Asked Questions
Is BMI accurate for muscular people?
No. BMI cannot differentiate between lean muscle mass and body fat. A bodybuilder and an obese person of the same height and weight will have identical BMI scores despite very different body compositions. For example, many professional athletes have BMIs in the "overweight" or "obese" range despite having very low body fat. If you're muscular, consider using body fat percentage or waist-to-hip ratio as complementary metrics.
What's the BMI formula?
In metric units: BMI = weight (kg) ÷ height² (m²). In imperial: BMI = (weight in pounds × 703) ÷ height² (in inches). The result is a dimensionless number used for classification. For example, a person who is 170 cm tall and weighs 70 kg would have a BMI of 70 ÷ (1.7²) = 24.2, placing them in the "normal weight" category just under the overweight threshold.
Are there better alternatives to BMI?
Waist-to-hip ratio, body fat percentage (via DEXA scan or calipers), and waist circumference are more nuanced measures. However, BMI remains popular because it requires no special equipment and correlates reasonably well with health outcomes at the population level. A DEXA scan costs $50–$150 and gives precise fat/muscle/bone breakdown, while a simple waist measurement above 40 inches (men) or 35 inches (women) is a strong independent risk factor regardless of BMI.
