BMI Calculator
Free BMI calculator with NIH health categories, body fat estimate, and ideal weight range. Instant results, mobile-friendly, free account available.
BMI at a glance
Free BMI calculator with NIH health categories, body fat estimate, and ideal weight range. Instant results, mobile-friendly, free account available.
This page computes the measurement directly: instead of quoting a population average, the BMI asks for your measurements and computes the index for your own body.
If you log meals, this is the companion number: it uses the same units and daily framing as the diary, which makes comparing your intake against the target a one-glance check rather than a conversion exercise.
What BMI tells you about your health
Body Mass Index (BMI) is the most widely used screening metric for identifying whether an adult's weight falls in a healthy range relative to their height. Developed in the 1830s by Belgian statistician Adolphe Quetelet and adopted by the World Health Organization in the 1980s, BMI provides a quick, reproducible number that correlates strongly with body fat percentage across large populations.
The BMI formula is the ratio of weight to height squared: weight (kg) / height (m)². Our calculator handles both unit systems automatically and returns your BMI value, the corresponding NIH weight category, an estimated body fat percentage using the Deurenberg equation, and your ideal weight range.
How to read your BMI result
BMI categories are standardized by the NIH and WHO. A BMI between 18.5 and 24.9 is considered healthy for most adults. Values below 18.5 suggest underweight. Values of 25 or higher indicate overweight or obesity, both linked to elevated risks of cardiovascular disease, type 2 diabetes, certain cancers, and all-cause mortality.
The muscle mass problem
BMI's biggest limitation is that it cannot distinguish between muscle and fat. Very muscular individuals often register as "overweight" despite low body fat. For a more complete picture, pair your BMI with our body fat calculator and waist-to-hip ratio.
Formula sources, population limits, and references for this body composition calculator are documented in our public methodology. Read the methodology · Medical disclaimer