BMI Calculator — Body Mass Index

What the BMI calculator does

Body Mass Index (BMI) is a quick screening number that relates your weight to your height. It is used worldwide by clinicians and public-health bodies such as the WHO and CDC to flag whether an adult may be underweight, at a healthy weight, overweight, or obese. This calculator works in both metric and imperial units and instantly returns your BMI, the category it falls into, and the healthy weight range for your height.

How the formula works

BMI divides your mass in kilograms by the square of your height in metres. Squaring height normalises body mass so that tall and short people can be compared on the same scale. If you enter imperial values they are converted to kilograms and centimetres before the calculation, so the result is identical either way.

How to interpret your result

The standard WHO cut-offs are: under 18.5 underweight, 18.5–24.9 normal, 25–29.9 overweight, and 30 or above obese. These bands estimate population-level health risk; they do not measure body fat directly. A person with high muscle mass can have a "high" BMI while carrying little fat, and an older adult can have a "normal" BMI while carrying excess fat. Treat BMI as a starting point, not a diagnosis.

Health recommendations

If your BMI sits outside the healthy range, small, sustainable changes — a modest calorie adjustment, regular movement, strength training, and better sleep — move it back over time. Use the Healthy Weight Range, TDEE, and Body Fat calculators alongside BMI for a fuller picture, and consult a healthcare professional before making major changes.