Work out your Body Mass Index from your height and weight, and see which category it falls into.
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Normal weight |
| 25.0 – 29.9 | Overweight |
| 30.0 and above | Obese |
BMI is a quick screening tool based on height and weight — it doesn't account for muscle mass, bone density, or body composition, so it's best used as a general guide rather than a full picture of health.
Enter your height and weight — in either metric (centimeters and kilograms) or imperial (feet/inches and pounds) units, depending on which toggle you select. Click Calculate, and the tool returns your BMI value along with the category it falls into. The calculation itself is straightforward: BMI equals weight in kilograms divided by height in meters squared (kg/m²), or for imperial units, weight in pounds multiplied by 703, divided by height in inches squared. You don't need to do this math yourself — the calculator handles the unit conversion and formula in one step.
BMI was developed in the 1830s by Belgian mathematician Adolphe Quetelet, originally as a way to study average body proportions across a population — not as an individual health diagnostic tool. It was adopted decades later by insurance companies and public health researchers because it's cheap and easy to calculate from just two numbers. The formula compares weight to the square of height because body weight tends to scale roughly with the square of height across a population, which makes BMI reasonably consistent for comparing large groups of people, even though it was never designed to evaluate a single individual's health precisely.
BMI uses only height and weight, so it can't distinguish between muscle, fat, bone, and water weight. Two people with identical height and weight — one a bodybuilder with low body fat and high muscle mass, the other sedentary with higher body fat and less muscle — will get the exact same BMI score, despite having very different health profiles. This is why athletes and heavily muscled individuals are frequently classified as "overweight" or even "obese" by BMI despite having low body fat percentages. BMI also doesn't account for where fat is stored on the body, even though visceral fat (around the organs) carries different health risks than fat stored elsewhere.
The standard BMI categories were developed primarily using data from adult populations and don't automatically adjust for age or biological sex, even though body composition naturally differs between these groups. Older adults tend to carry more fat relative to muscle at the same BMI as younger adults. Some health organizations also use different BMI cutoffs for certain ethnic populations — for example, several Asian health guidelines use lower BMI thresholds for "overweight" and "obese" because research has shown health risks can appear at lower BMI values in some Asian populations compared to the standard Western cutoffs.
Because of its limitations, most health professionals recommend treating BMI as one data point among several rather than a standalone diagnosis. Waist circumference is a useful companion measurement, since it reflects abdominal fat more directly than BMI alone. Body fat percentage — measurable through methods like skinfold calipers, bioelectrical impedance scales, or the Navy circumference method — gives a more direct picture of body composition. Blood pressure, resting heart rate, cholesterol, and blood sugar levels are all better indicators of metabolic health than BMI on its own. If your BMI falls outside the "normal" range but these other markers look healthy, that's worth discussing with a doctor rather than assuming the BMI number alone tells the full story.
A single BMI reading is a snapshot, but tracking it over months or years can reveal useful trends even given its limitations — a steady upward or downward trend often reflects real changes in body composition, especially when paired with how your clothes fit or how you feel physically. Sudden, large swings in BMI over a short period are worth discussing with a doctor, since rapid weight change can sometimes signal an underlying health issue rather than intentional lifestyle changes. As a general planning tool, checking BMI every few months alongside other health markers gives a more complete picture than relying on any single measurement in isolation.
Is BMI accurate for children? No — this calculator is designed for adults. Children and teens require age- and sex-specific BMI percentile charts, since body composition changes significantly during growth.
Can BMI be used during pregnancy? Standard adult BMI categories don't apply during pregnancy, since weight gain is expected and healthy. Pregnant individuals should follow weight guidance from their healthcare provider instead.
Why do I have a "normal" BMI but still have health concerns? BMI can miss cases of high body fat percentage with low muscle mass, sometimes called "normal weight obesity." Body composition testing gives a clearer picture in these cases.
Is a lower BMI always healthier? Not necessarily. Being significantly underweight carries its own health risks, including nutritional deficiencies and weakened immune function. The goal is a healthy range, not the lowest possible number.
Should I recheck my BMI often? Checking every few months is usually enough, since meaningful body composition changes take time — daily fluctuations mostly reflect water weight rather than any real change.
Does gender affect what a 'healthy' BMI looks like? The standard BMI categories are applied the same way regardless of sex, though body composition differences between men and women mean the number can reflect somewhat different things physically.
Does clothing or time of day affect a weight-based BMI reading? Yes, slightly — weighing at a consistent time (like first thing in the morning, minus heavy clothing) gives more comparable readings over time than weighing at random points during the day.
Is there a BMI calculator specifically for athletes? Not as a separate standard formula — the same BMI math applies, though the resulting category should be interpreted with more caution given how muscle mass skews the number for very athletic individuals.
Last reviewed by Mehmed on July 11, 2026.