BMI Calculator
Calculate your Body Mass Index (BMI) and understand your weight category.
About BMI (Body Mass Index)
Body Mass Index (BMI) is a widely used screening tool that estimates body fat based on your height and weight. Developed by Belgian mathematician Adolphe Quetelet in the 1830s, it remains one of the quickest ways to gauge whether a person falls into an underweight, normal, overweight, or obese category. While it does not measure body fat directly, BMI serves as a useful starting point for health assessments.
BMI Formula
Metric: BMI = weight (kg) ÷ height² (m²)
Imperial: BMI = (weight (lb) ÷ height² (in²)) × 703
For example, a person weighing 70 kg who is 1.75 m tall has a BMI of 70 ÷ (1.75 × 1.75) = 22.9, which falls in the "Normal" range.
BMI Categories
- Underweight: BMI below 18.5 — may indicate nutritional deficiency
- Normal weight: BMI 18.5–24.9 — associated with the lowest health risks
- Overweight: BMI 25–29.9 — increased risk of cardiovascular issues
- Obese: BMI 30 or above — significantly elevated health risks
Limitations of BMI
BMI does not differentiate between muscle mass and body fat. Athletes, bodybuilders, and individuals with dense bone structures may register as "overweight" despite having low body fat. Additionally, BMI does not account for fat distribution — abdominal fat carries higher health risks than fat stored in the hips or thighs. Age, sex, and ethnicity can also influence how BMI relates to actual health outcomes.
Alternatives to BMI
For a more complete picture of body composition, consider these alternatives: body fat percentage (measured via calipers, bioelectrical impedance, or DEXA scans), waist-to-hip ratio (a predictor of cardiovascular risk), and waist circumference (values above 40 inches for men or 35 inches for women indicate higher risk). Using BMI alongside these metrics gives a more balanced view of overall health.
Frequently Asked Questions
A BMI between 18.5 and 24.9 is generally considered healthy for most adults. Below 18.5 is classified as underweight, 25–29.9 as overweight, and 30 or above as obese.
BMI can overestimate body fat in athletes and people with high muscle mass because it does not distinguish between muscle and fat. Additional measures such as body fat percentage or waist-to-hip ratio provide a more complete picture.
BMI is calculated by dividing your weight in kilograms by your height in metres squared. In imperial units, divide weight in pounds by height in inches squared and multiply by 703.
Alternatives include body fat percentage measured via calipers or DEXA scans, waist-to-hip ratio, waist circumference, and the body adiposity index. These methods provide more nuanced insight into body composition.