BMI Calculator (kg & cm) by Age and Gender

In metric units, BMI = weight (kg) ÷ height (m)². In imperial units, BMI = (weight (lb) ÷ height (in)²) × 703. For example, a person who is 1.75 m and 70 kg has a BMI of 70 ÷ (1.75 × 1.75) = 22.9, which falls in the healthy range. In imperial units, someone who is 5 ft 9 in (69 in) and 154 lb works out to (154 ÷ 69²) × 703 = 22.7 — the same result, just rounded differently because of unit conversion. The two formulas always agree once you convert units consistently, so pick whichever matches the units on your bathroom scale and tape measure. The calculator above runs either formula instantly and also shows your category on a colour-coded chart, so you don't need to do the arithmetic by hand unless you want to double-check it.

For most adults, the World Health Organization's classification puts 18.5 to 24.9 in the healthy range. Below 18.5 is underweight, 25 to 29.9 is overweight, 30 to 39.9 spans Obesity Class I and II, and 40 or above is Obesity Class III. For example, someone who is 1.70 m tall is in the healthy range between roughly 53 kg and 72 kg. BMI is a population-level screening tool, not a diagnosis, so a single number in or out of range doesn't tell the whole story — pair it with waist circumference (a marker for visceral fat), blood pressure, blood sugar, and activity level for a fuller picture, and treat a borderline result as a prompt to check in with a doctor rather than a verdict.

Your BMI estimates whether your weight is under, healthy, over, or in the obesity range relative to your height, using the same weight-to-height-squared formula doctors and public health agencies have used for decades. A higher BMI is statistically linked with greater risk of conditions like type 2 diabetes, high blood pressure, and cardiovascular disease — for example, research consistently shows the risk of type 2 diabetes roughly doubles as BMI rises from the healthy range into the obese range. A very low BMI (under 18.5) can signal undernutrition or an underlying health issue instead. The key caveat: BMI is an indicator based on population averages, not an individual diagnosis, so it should always be read alongside other health markers rather than in isolation.

No — for adults aged 20 and over, BMI uses the exact same formula and the exact same category thresholds (18.5, 25, 30) for men and women. What differs is body composition: women typically carry a higher percentage of essential body fat (roughly 10-13%) than men (roughly 3-5%) at the same BMI, so two people with an identical BMI of, say, 24 can have noticeably different muscle-to-fat ratios depending on sex. Some national health bodies also apply lower BMI risk thresholds for certain ethnic groups (for example, parts of Asia use 23 instead of 25 as the overweight cutoff) because health risk at a given BMI can vary by population — but the calculation itself never changes by gender.

For adults aged 20 and older, the standard healthy range of 18.5-24.9 applies fairly consistently across age groups, though some clinicians allow a slightly higher target (up to around 27) for adults over 65, since a small buffer above 'healthy' is linked to better resilience during illness and a lower risk of frailty in older age. For anyone under 20, adult BMI categories don't apply at all — children and teens must be plotted on age- and sex-specific growth percentile charts (like the CDC or WHO growth charts), because what counts as a healthy BMI for a 10-year-old is very different from a 17-year-old. Always use a pediatric growth chart, not this adult calculator, for anyone under 20.

A healthy weight is whatever weight keeps your BMI between 18.5 and 24.9 for your specific height — there's no single 'ideal number' that applies to everyone the same height, since frame size and muscle mass vary. For example, at 1.65 m (5 ft 5 in), the healthy BMI range works out to roughly 50-68 kg (about 112-150 lb); at 1.80 m (5 ft 11 in), it's roughly 60-81 kg (about 132-178 lb). Enter your own height in the calculator above and it instantly shows your personal healthy weight range in both kilograms and pounds, plus where your current weight sits on the chart, so you don't have to do the range math yourself.

The safest approach is a moderate, sustained calorie deficit rather than a crash diet: cutting roughly 500 calories a day from your maintenance level typically produces about 0.5 kg (1 lb) of fat loss per week, which is widely considered a sustainable pace that preserves muscle mass. Pair that with at least 150 minutes of moderate activity per week (brisk walking, cycling, swimming) plus two sessions of resistance training to protect muscle while you lose fat, 7-9 hours of sleep (poor sleep is linked to higher hunger hormones), and basic stress management, since chronic stress raises cortisol and can drive fat storage. Avoid very-low-calorie crash diets — they often cause muscle loss alongside fat loss and are hard to maintain, so the weight tends to return. If you have a medical condition or a large amount of weight to lose, loop in a doctor before changing your diet significantly.

Not always — BMI only looks at weight relative to height, so it cannot distinguish muscle from fat or show where fat is stored on the body, which means it can misclassify several groups. A bodybuilder who is 1.80 m and 95 kg with low body fat can score a BMI of 29.3 ('overweight') despite being lean and athletic, simply because muscle is denser than fat. Pregnant women, older adults who have lost muscle mass (sarcopenia), and some ethnic groups with different typical body compositions can also be misclassified in either direction. Use BMI as a quick starting point and pair it with waist circumference, blood pressure, blood sugar, and lipid panels for a much more reliable picture of metabolic health than BMI alone can provide.

Yes. It is completely free with no signup, and the calculation runs entirely in your browser — your height, weight, age, and gender are never sent to a server.