BMI Calculator computes body mass index from your weight and height, in either metric (kilograms and centimeters) or imperial (pounds, feet, and inches) units, and shows which of the four standard WHO categories — underweight, normal weight, overweight, or obese — your result falls into.

BMI is a widely used screening measure, but it's a simple ratio of weight to height and doesn't account for muscle mass, bone density, or body composition. This tool is provided for informational purposes only and is not a substitute for professional medical advice.

The underlying formula is intentionally simple: BMI = weight (kg) ÷ height (m)² for metric input, or the equivalent 703 × weight (lb) ÷ height (in)² for imperial input — a conversion factor that adjusts for pounds and inches instead of kilograms and meters so both unit systems produce the same numeric result for the same person. Switching between metric and imperial mid-entry doesn't clear what you've already typed; the tool converts your existing values on the fly so you can compare how a measurement reads in either system without starting over.

The four category thresholds shown — under 18.5, 18.5 to 24.9, 25 to 29.9, and 30 and above — are the standard adult ranges published by the World Health Organization, used here exactly as published rather than a modified or proprietary scale. It's worth repeating why the FAQ below flags this explicitly: BMI was designed as a population-level screening tool for epidemiological studies, not an individual diagnostic measure, so an athlete with a high muscle-to-fat ratio can land in an "overweight" BMI category despite having low body fat. Treat the number as a starting point for a conversation with a healthcare provider, not a conclusion on its own.

As with every calculator on this site, the figures you enter — your weight and height — are used only to compute the on-screen result and are never transmitted anywhere or saved beyond your current session.