BMI Calculator

BMI (Body Mass Index) is a quick screen of whether your weight is healthy for your height. It's used worldwide by doctors and insurers, though it's a screening tool — not a diagnosis.

The formula

BMI = weight (kg) ÷ height (m)²

Height must be in metres, so divide centimetres by 100. For a 70 kg, 175 cm person:

BMI = 70 ÷ (1.75)² = 70 ÷ 3.06 = 22.9

Where BMI comes from

BMI has an unexpected origin: it was devised in the 1830s by the Belgian statistician Adolphe Quetelet, who noticed that across populations, body weight tends to rise in proportion to the square of height. The index was later renamed the Body Mass Index in the 1970s and adopted as a population-level screening tool. That history matters — it was built to describe large groups, not to judge a single individual, and it was never designed as a measure of body fat. Over the decades the categories you see here have been refined (notably by the World Health Organization in the 1990s), but the underlying math has barely changed in almost two centuries.

BMI categories (WHO, adults)

A 22.9 result sits comfortably in the normal range. For a 175 cm person, a normal BMI of 18.5–24.9 corresponds to a healthy weight of roughly 56.7–76.3 kg — the calculator shows your exact range. Because the formula squares your height, taller people can carry several extra kilograms within the same category — each centimetre of height expands the healthy range faster than you might expect.

What your number actually tells you

Think of BMI as a flag, not a verdict. A reading well inside the normal band is reassuring for most people, while a high reading (especially above 30) is a reasonable prompt to look more closely at diet, activity and any family history of metabolic problems. Crucially, BMI is correlated with health at the population level but not destiny for any one person. Two people can share the same BMI yet differ enormously in fitness, muscle mass and cardiometabolic risk, which is why doctors rarely rely on BMI alone.

Common misconceptions

• "A low BMI is always healthy." Very low readings can reflect malnutrition, disordered eating or an underlying illness, not fitness.
• "BMI measures fat directly." It does not — it only combines height and weight, so a lean bodybuilder and an untrained person of the same size can get the same number.
• "Normal BMI means no health risk." Someone with a "normal" BMI but a large waist and high blood pressure can still be at raised metabolic risk, which is why the next section matters.

Limits of BMI

BMI cannot distinguish muscle from fat, so it can overestimate body fat for athletes and underestimate it for older adults or people with low muscle mass. It also doesn't account for where fat sits (belly fat is riskier). For a fuller picture, combine BMI with waist circumference and, ideally, a body-fat measurement. BMI for children and teens uses age- and sex-specific charts, so the adult categories above don't apply. This tool is for general information and is not a medical diagnosis — if you have concerns about your weight, speak to a healthcare professional.