BMI Calculator

Calculate Body Mass Index free online from height and weight, with category classification. A screening tool with known limitations, not a complete health assessment.

Height (cm)

Weight (kg)

Browser only. A general screening tool, not a complete health assessment -- consult a healthcare provider for personalized guidance.

How to Use This Tool

Choose your unit systemMetric or imperial

Enter height and weightUse your current measurements

See your BMI and categoryWith context on its known limitations

A Widely Used Screening Tool With Well-Documented Limitations

BMI's appeal is its simplicity -- one formula, one number, population-wide standardized categories. That same simplicity is exactly why it doesn't capture the full health picture for every individual, since it cannot distinguish muscle mass from fat mass or account for where body fat is distributed, both of which matter for actual health risk.

Why a Muscular Athlete Might Show "Overweight"

BMI uses only height and weight, with no input for body composition. A bodybuilder with low body fat but substantial muscle mass will often calculate into the "overweight" or even "obese" category despite being in excellent physical condition -- a well-known and frequently cited limitation of the formula.

Using BMI Appropriately -- As One Signal, Not a Verdict

BMI remains useful as a quick, standardized population-level screening indicator, which is why it's still widely used in healthcare settings as a starting point. For an individualized health assessment, combining BMI with other measures and a conversation with a healthcare provider gives a far more complete and accurate picture than this number alone.

Frequently Asked Questions

BMI = weight (kg) / height (m)^2. For imperial units, BMI = 703 x weight (lb) / height (in)^2. Both produce the same standardized BMI scale used for population-level health screening.

Under 18.5 is classified underweight, 18.5-24.9 normal weight, 25-29.9 overweight, and 30+ obese, according to World Health Organization classifications widely used for general population screening.

BMI doesn't distinguish between muscle mass and fat mass, which means very muscular individuals (athletes, bodybuilders) often show as 'overweight' or 'obese' despite having low body fat, while it can also underestimate health risk in some people with normal BMI but high visceral fat.

No, the standard adult BMI formula uses the same calculation and thresholds regardless of age, sex, or muscle mass, which is exactly why it's considered a population screening tool rather than an individualized health assessment.

BMI is best used as one general screening indicator among several, not a definitive individual health verdict. Discussing your specific health picture with a healthcare provider, who can consider body composition, medical history, and other factors, gives a much more complete and individualized assessment.