BMI Calculator

For most adults, a BMI between 18.5 and 24.9 is classified as the healthy weight range. Below 18.5 is underweight, 25 to 29.9 is overweight, and 30 or above is classified as obesity. These four bands make up the standard adult BMI chart, and they come from population health research, applying equally to adult men and women, though they are interpreted differently for children and teenagers.

Rearrange the same formula instead of solving it forward: target weight in pounds equals the BMI you want, times your height in inches squared, divided by 703 (or, in metric, target weight in kg equals BMI times height in metres squared). For someone 70 inches tall aiming for the middle of the healthy range, a BMI of 22 works out to 22 × 4,900 ÷ 703, about 153 pounds. This is sometimes called a reverse BMI calculation.

No, not reliably. BMI cannot tell muscle from fat, and muscle is denser, so athletes and people who strength-train regularly often land in the overweight category despite low body fat. A commonly cited example: an Olympic sprinter and a sedentary person of identical height and weight can post the same BMI, even though their health profiles are nothing alike. Body fat percentage or waist-to-height ratio reads them more accurately.

BMI only compares weight to height squared; it never measures fat directly. Body fat percentage estimates the actual proportion of your weight that is fat tissue, typically measured with calipers, bioelectrical impedance scales, or a DEXA scan. Because it accounts for composition rather than total mass, body fat percentage tracks cardiovascular and metabolic risk more precisely than BMI, but it needs equipment BMI doesn't, which is why BMI remains the more common first-pass screen.

For some purposes, yes. Waist-to-height ratio divides waist circumference by height and reflects where fat is stored, specifically the visceral fat around the abdomen that BMI cannot see at all. Research reviewed in a 2016 meta-analysis found it predicts cardiovascular risk more consistently than BMI, including in people BMI classifies as a healthy weight. A commonly cited target is keeping waist circumference under half your height.

Yes. A World Health Organization expert consultation found that Asian populations tend to face higher health risks at lower BMI values than the standard adult thresholds capture, so several health bodies use lower cutoffs, around 23 for overweight and 27.5 for obesity, specifically for Asian populations. The standard 25 and 30 thresholds were built primarily from data on European and North American adults.

No. The underlying formula came from Adolphe Quetelet, a 19th-century statistician studying average body proportions across populations, not individual patients. It was renamed body mass index in the 1970s as a fast, equipment-free way to flag population-level obesity trends in research. Using it to make a definitive call about one specific person's health was never its original purpose, which is why it works better as a screening cue than a diagnosis.

The BMI formula in pounds and inches is your weight times 703, divided by your height in inches squared. For example, someone weighing 180 pounds at 70 inches tall works out to 703 times 180, divided by 4,900, giving a BMI of about 25.8. The 703 factor exists purely to convert imperial units onto the metric kilograms-per-square-metre scale that BMI is defined in.

Not the same way as for adults. Children and teens are measured against BMI-for-age percentile charts specific to their sex, since normal body composition changes constantly as kids grow. The fixed 18.5 to 24.9 healthy range on this page applies to adults only; separate child and teen BMI tools compare a young person's number against others their own age and sex instead of one flat cutoff.

It's a reasonable starting screen, not a full picture. BMI is fast, free, and correlates with health risk across large populations, which is why clinicians still use it as a first check. But it says nothing about muscle mass, fat distribution, blood pressure, or metabolic markers, and health agencies describe it as a screening tool, not a diagnostic one. Pair it with a waist measurement or a clinician's assessment for a fuller read.

Yes, but with real caveats now. In 2023 the American Medical Association adopted a policy calling BMI an imperfect clinical measure and urging physicians to combine it with other markers, such as waist circumference, body composition, and metabolic factors, rather than relying on it alone. It remains the fastest, cheapest first-pass screen available, which is why it is still used, just less often as a standalone verdict.

No. The formula and the 18.5 to 24.9 healthy range are identical for adult men and women, with no separate chart. The nuance is in interpretation: at the same BMI, women on average carry a higher body fat percentage than men, since men tend to hold more lean muscle. That does not change the BMI number or its category, but it explains why two people with an identical BMI can have different body compositions.

BMI Prime is your BMI divided by 25, the upper boundary of the healthy weight range, expressed as a ratio instead of a raw number. A BMI Prime of exactly 1.0 sits right on that boundary; below 1.0 means you're under it, above 1.0 means you're over it by that proportion. A BMI of 27.5, for example, gives a BMI Prime of 1.1, meaning it's 10% above the healthy-range ceiling. It's the same underlying BMI figure presented differently, not a separate measurement, and it carries the same muscle-versus-fat limitation as standard BMI.

The Ponderal Index divides weight by height cubed instead of height squared, which makes it react less sharply to height differences than BMI. It's used mainly in neonatal and fetal-growth research: a 1991 study in the Australian and New Zealand Journal of Obstetrics and Gynaecology found it identified at-risk term infants more reliably than birth weight for gestational age alone. For adults, it isn't part of routine clinical practice the way BMI and waist-to-height ratio are, which is why this calculator reports standard adult BMI rather than adding it as a second figure.