BMI Calculator
Calculate your Body Mass Index and see your healthy weight range in seconds.
Your BMI
Healthy Weight Range
56.7 – 76.3 kg
For your height, a BMI of 18.5–24.9
BMI is a general screening tool, not a diagnosis. It doesn't account for muscle, bone density, or body composition. Consult a doctor for health advice.
BMI is simultaneously the most widely used health metric in the world and one of the most criticized, and both facts deserve explanation. It was devised in the 1830s by a Belgian statistician studying populations, not patients — he was explicitly not trying to diagnose individuals. It survives because it is free, instant, and correlates well with health outcomes across large groups. It fails because it cannot distinguish muscle from fat, ignores where fat sits on your body, and was calibrated on European populations. This calculator gives you the number and, more usefully, the context needed to know what it does and does not mean for you.
How the calculator works
Enter your height and weight in either metric or imperial units. The calculator divides weight by height squared and places the result in the standard World Health Organization categories. It also shows the weight range corresponding to a BMI of 18.5 to 24.9 for your height, which is often more actionable than the single number — it tells you the target rather than just the verdict.
The formula
Metric: BMI = weight(kg) ÷ height(m)²
Imperial: BMI = 703 × weight(lb) ÷ height(in)²
Categories (WHO):
Under 18.5 Underweight
18.5 – 24.9 Normal
25.0 – 29.9 Overweight
30.0 and over Obese
Example: 70 kg, 1.75 m → 70 ÷ 3.0625 = 22.9The height-squared term is where the criticism starts. Human bodies scale in three dimensions, not two, so squaring rather than cubing systematically overestimates BMI for tall people and underestimates it for short people. Quetelet chose the square because it fit population averages of his era, not because it reflects any biological principle. This is a known limitation that has never been fixed, largely because the categories are now embedded in decades of research.
What to know about BMI
- 1BMI cannot tell muscle from fat, which is its most consequential flaw. A muscular athlete frequently registers as overweight or obese while carrying very low body fat. The number measures mass relative to height and has no way of knowing what that mass is made of.
- 2Waist circumference often predicts risk better than BMI. Visceral fat around the organs is metabolically dangerous in a way that fat elsewhere is not. A waist over 94 cm for men or 80 cm for women signals elevated risk regardless of what BMI says — two people at the same BMI can have very different outcomes based on distribution alone.
- 3The thresholds differ by ethnicity. Health risk begins at lower BMI values for South Asian and East Asian populations, and several health authorities use 23 rather than 25 as the overweight threshold for these groups. The standard categories were derived from European data and are not universal.
- 4BMI is unreliable for children, pregnant women, and the elderly. Children are assessed with age-and-sex percentile charts instead. Older adults lose muscle and bone density, so a BMI that reads as "normal" can conceal significant fat gain and muscle loss happening simultaneously.
- 5Treat BMI as a screening signal, not a diagnosis. It is genuinely useful for spotting trends across populations and for prompting a closer look at an individual. It is not useful as a verdict on one person's health, and no competent clinician uses it that way in isolation.
Frequently asked questions
Is BMI accurate?
It is accurate as a population statistic and unreliable as an individual diagnosis. Across large groups, BMI correlates well with health outcomes, which is why epidemiologists still use it. For one person it can be badly wrong in either direction — muscular people are misclassified as overweight, and people with low muscle mass can sit in the normal range while carrying unhealthy body fat.
Why is BMI unreliable for athletes?
Because muscle is denser than fat, so a muscular body weighs more for the same volume. A rugby player at 100 kg and 1.80 m has a BMI of 30.9, formally obese, while potentially carrying under 10% body fat. BMI measures total mass against height and has no mechanism for distinguishing what that mass consists of.
What is a healthy BMI range?
The WHO defines 18.5 to 24.9 as normal, but this range was derived largely from European populations and is not universally applicable. Several authorities recommend an upper limit of 23 for South Asian and East Asian populations, where metabolic risk begins earlier. Body composition, waist circumference, and fitness matter more than sitting inside or outside the range.
What is a better alternative to BMI?
Waist-to-height ratio is a strong, equally simple alternative — keeping your waist under half your height works across ethnicities and captures the visceral fat that actually drives risk. For more precision, body fat percentage via DEXA or bioelectrical impedance measures composition directly. Even a tape measure around the waist beats BMI for individual risk assessment.
Why does BMI use height squared instead of cubed?
Because Quetelet found that the square fit population data of the 1830s better than the cube, not for any biological reason. Since bodies scale in three dimensions, the square systematically favors short people and penalizes tall ones. Alternatives like the Ponderal Index use height cubed and are arguably more sound, but BMI's categories are embedded in decades of research and clinical guidance, so the flawed version persists.