BMI Calculator

This is the World Health Organization's standard BMI classification for adults aged 20 and over, used the same way for men and women. It's the same table CDC.gov and most clinical references use.

In metric units, BMI equals weight in kilograms divided by height in meters squared. For example, a person weighing 70 kg at 1.75 m tall: 70 ÷ (1.75 × 1.75) = 70 ÷ 3.0625 = 22.9, which falls in the normal weight range.

In US/imperial units, BMI equals 703 × weight in pounds, divided by height in inches squared. The same person at roughly 154 lb and 5'9" (69 in): 703 × 154 ÷ (69 × 69) = 108,262 ÷ 4,761 = 22.7. The small difference from the metric result is just unit-rounding, not a different measurement.

BMI measures excess weight, not excess body fat, so it can't tell the difference between muscle and fat on its own. A muscular athlete and a sedentary person of the same height and weight get the identical BMI, even though their actual health risk can be very different. The CDC's own guidance notes that older adults tend to carry more body fat than younger adults at the same BMI, and women tend to carry more body fat than men at the same BMI too, so the number alone doesn't capture either difference.

None of this makes BMI useless. For most of the adult population it correlates reasonably well with body fat and real health risk, which is exactly why it's still the standard first-pass screen. It just means BMI works best as a starting point, not a final answer. If you're a visibly muscular athlete, our BMI Calculator with Body Fat % Comparison factors that in directly instead of relying on weight and height alone.

According to the CDC, carrying excess weight is linked to a higher risk of high blood pressure, type 2 diabetes, coronary heart disease, stroke, certain cancers, sleep apnea, and osteoarthritis. Being underweight carries its own real risks too: nutrient deficiencies, weakened immune function, osteoporosis, and, in women, a higher chance of first-trimester pregnancy complications.

• Overweight/obesity: cardiovascular disease, type 2 diabetes, several cancers, joint problems, and sleep apnea
• Underweight: nutrient deficiencies, reduced bone density, weakened immunity, and reproductive health effects
• Both directions are linked to a higher overall mortality risk than a normal-weight BMI in most population studies

A single out-of-range BMI reading isn't a diagnosis of any of these conditions on its own. It's a signal worth discussing with a doctor, especially alongside other factors like waist circumference, family history, and lifestyle.

This adult BMI scale doesn't apply well to several groups, each of which genuinely needs a different reference range rather than just a different message on the same chart. Children and teens are measured against an age- and sex-specific growth percentile, not a fixed adult range, since a healthy BMI for an 8-year-old and a 17-year-old are very different numbers. Pregnancy changes healthy weight-gain targets entirely. Older adults and highly muscular athletes both tend to get systematically mismeasured by the plain adult scale, in opposite directions.