BMI Calculator

This calculator applies the standard Body Mass Index formula, weight in kilograms divided by height in meters squared, and classifies the result against a seven-band scale rather than the simplified four. The exact cutoffs are: Severely Underweight below 16, Underweight 16 to 18.5, Normal 18.5 to 25, Overweight 25 to 30, Obese Class I 30 to 35, Obese Class II 35 to 40, and Obese Class III at 40 and above. The computed BMI is shown to one decimal place along with the matching category, and a horizontal scale renders all seven bands as equal-width segments (each 100/7, about 14.29 percent wide) with a pointer positioned proportionally within the band where your value falls.

Both metric and imperial entry are supported, and the conversion happens internally with explicit constants. In imperial mode pounds are multiplied by 0.453592 to get kilograms, and height entered as feet plus inches is summed as total inches and multiplied by 0.0254 to get meters; metric mode simply divides centimeters by 100. Inputs are sanitized to digits with at most one decimal place and capped (weight at 500, metric height at 300 cm, feet at 9, inches at 11, age at 120), so out-of-range or malformed entries are rejected before any calculation runs. Beyond the BMI number itself, the tool back-solves your ideal weight range by evaluating 18.5 times height squared and 25 times height squared, then converts those bounds back to pounds when imperial is active, and when your BMI sits below 18.5 or at or above 25 it reports the exact weight you would need to gain or lose to reach the Normal band.

The age and gender fields are deliberately reference-only: the component states explicitly that the standard weight-over-height-squared formula does not vary by age or sex, so toggling Male/Female or entering an age changes nothing in the result (they are excluded from the memoized calculation entirely). The interface also surfaces the well-known limitations of BMI as a screening rather than diagnostic measure, noting that it ignores muscle mass, bone density, and fat distribution and that athletes can register a high BMI from muscle alone. Calculations run live in the browser via a memoized computation that recomputes only when weight, height, or unit system change.