BMI Calculator

Body Mass Index is weight divided by height squared — BMI = weight (kg) / height (m)², the standard WHO formula. It is a quick screening ratio of weight to height, not a measure of body fat or health directly. It puts a single number on whether your weight is high or low for your height — useful at population scale, but it says nothing about what that weight is made of.

The general WHO bands: below 18.5 underweight, 18.5–24.9 normal, 25.0–29.9 overweight, and 30.0+ obese. These cutoffs are the same regardless of age or sex — part of their limitation, since they treat a muscular athlete and a sedentary person of the same height and weight identically.

Because BMI only knows your weight and height — not whether that weight is muscle or fat. A muscular person can read as “overweight” despite low body fat, while an older person who has lost muscle can read as “normal” while carrying excess fat. BMI also ignores where fat sits, and abdominal fat is the metabolically risky kind. It is a screening tool, not a body-composition measure.

BMI is cheap, fast, and needs only a scale and a tape measure, which makes it a reasonable first-pass screen — at the population level it correlates with outcomes well enough to be useful. The problem is only when it is treated as the final word for an individual. Used as one input among several, it still has a place.

Two things BMI misses: how much of your weight is fat, and where that fat sits. The Waist Ratio tools capture abdominal (visceral) fat, and the Body Fat Estimator tells you the muscle-versus-fat split BMI cannot see. Reading them together beats the single number alone.