Util Tools What is BMI?
Body Mass Index (BMI) is a simple ratio of weight to height used to place adults into broad weight categories. The formula is BMI = weight (kg) / height (m)2, or in imperial units, weight (lb) / height (in)2 multiplied by 703. It is quick, free, and needs only a scale and a tape measure, which is why doctors and researchers use it as a first-pass screening tool.
BMI categories
The World Health Organization defines these adult ranges:
- Under 18.5: underweight
- 18.5 to 24.9: healthy weight
- 25.0 to 29.9: overweight
- 30.0 and above: obese
What BMI does not tell you
BMI is a population screening tool, not a diagnosis, and it has real limitations. Because it uses only height and weight, it cannot tell muscle from fat, so a muscular athlete may register as "overweight" despite low body fat, while someone with little muscle may sit in the healthy range yet carry excess fat. It also does not account for where fat is stored, age, or ethnicity, all of which affect health risk.
Using BMI sensibly
Treat BMI as one data point among several. For a fuller picture, combine it with waist circumference, body-fat percentage, and how you feel and function. BMI is the same calculation for men and women, and "BMI prime" is simply your BMI divided by 25, showing how far you are above or below the top of the healthy range.
This calculator is for general information only and is not medical advice. Consult a healthcare professional about your weight and health.
Last updated: July 2026