BMI Calculator

Body mass index is a single number that relates weight to height. It was designed for describing populations and is used by WHO and national health agencies as a screening measure because it needs only two measurements that are easy to take. It says how heavy someone is for their height and nothing else: it does not measure body fat, muscle, bone or where weight sits on the body.

HeightViz shows the number, the band it falls in as published by the sources below, and the weight range for the same height that would land in the 18.5 to 24.9 band. It does not interpret the result or suggest what anyone should weigh.

BMI is weight in kilograms divided by height in metres squared. For 75 kg and 175 cm: the height is 1.75 m, squared is 3.0625, and 75 ÷ 3.0625 = 24.5. The calculator rounds to one decimal place, which is the precision the published tables use.

Heights typed in feet and inches or metres and weights typed in pounds are converted exactly first, at 2.54 cm per inch and 0.45359237 kg per pound, so the result does not depend on the units you use.

WHO's Global Health Observatory defines its adult indicators as underweight below 18.5, overweight at 25 and above, and obesity at 30 and above. The CDC publishes the same cut-points for adults aged 20 and over, names 18.5 to under 25 "healthy weight", and divides obesity into three classes.

Turning the cut-points around gives the weight range for a height: multiply the height in metres by itself, then by 18.5 for the lower bound and 24.9 for the upper bound. For 175 cm that is 56.7 kg to 76.3 kg (125 lbs to 168 lbs). The height–weight chart lists this range for every height from 140 to 210 cm.

Because it uses only height and weight, BMI cannot distinguish muscle from fat: two people with the same BMI can have very different bodies. It also does not account for age, sex, or how weight is distributed, and the adult cut-points do not apply to children and teenagers, whose BMI is read against growth references for their age and sex.

WHO and the CDC both describe BMI as a screening tool rather than a diagnostic one. HeightViz follows that: the calculator reports where a number falls on the published scale and leaves any interpretation to the reader and their clinician. To see how height and weight change a body's shape rather than a number, use the Body Visualizer.

• WHO Global Health Observatory, body mass index indicators — Indicator definitions: underweight BMI < 18.5, overweight BMI ≥ 25, obesity BMI ≥ 30. Checked 2026-09-20.
• CDC, Adult BMI Categories — Underweight < 18.5; healthy weight 18.5 to < 25; overweight 25 to < 30; obesity ≥ 30 (class 1: 30 to < 35, class 2: 35 to < 40, class 3: ≥ 40). Page updated 2024-03-19. Checked 2026-09-20.