A BMI of 30 or higher is the standard threshold for obesity in adults. BMI, or body mass index, is calculated by dividing your weight by your height squared, and it places you into one of several categories that clinicians use to screen for weight-related health risks. But that single number doesn’t tell the whole story, and recent guidelines emphasize that it should be one piece of a broader assessment.
BMI Categories for Adults
BMI is expressed as a number in kg/m². The standard adult categories are:
- Normal weight: 18.5 to 24.9
- Overweight: 25 to 29.9
- Class I obesity: 30 to 34.9
- Class II (serious) obesity: 35 to 39.9
- Class III (severe) obesity: 40 and above
These three obesity classes aren’t just labels. Each step up carries meaningfully higher health risks. Compared to people with a BMI between 22.5 and 24.9, those with a BMI of 35 to 39.9 face an 88 percent higher risk of death from any cause. At a BMI of 40 to 49.9, that risk is 2.5 times higher, according to a large pooling project from the National Cancer Institute.
How to Calculate Your BMI
If you’re working in pounds and inches, multiply your weight in pounds by 703, then divide by your height in inches squared. In metric units, divide your weight in kilograms by your height in meters squared. So a person who weighs 185 pounds and stands 5 feet 9 inches tall (69 inches) has a BMI of about 27.3, which falls in the overweight range. Most health websites and apps have built-in calculators that do this instantly.
Lower Thresholds for Some Populations
The standard cutoff of 30 was developed largely from data on European populations. For people of Asian descent, health risks like type 2 diabetes begin climbing at significantly lower BMI values, which is why several countries and medical organizations use different thresholds.
A joint recommendation from the World Health Organization’s Western Pacific office, the International Association for the Study of Obesity, and the International Obesity Task Force set the obesity threshold for Asian populations at 25, not 30. China uses 28 as its obesity cutoff, finding that this number identifies risk factors with roughly 90 percent specificity. Japan defines obesity starting at 25. India and other South Asian countries use 23 as the overweight threshold, the same point at which the American Diabetes Association recommends diabetes screening for Asian Americans.
These aren’t minor adjustments. A South Asian man with a BMI of 26 could be classified as normal weight under standard categories while already carrying enough body fat to raise his metabolic risk substantially. If you’re of Asian descent, the lower cutoffs are more relevant to your health than the standard chart.
BMI Works Differently for Children
For children and teens aged 2 through 19, BMI isn’t compared to fixed cutoffs. Instead, a child’s BMI is plotted against growth charts for their age and sex, producing a percentile ranking. The CDC defines overweight in children as a BMI at or above the 85th percentile but below the 95th, and obesity as the 95th percentile or above. A 10-year-old boy at the 96th percentile doesn’t necessarily have a BMI of 30. He simply has a higher BMI than 96 percent of boys his age on the reference chart.
Why BMI Alone Can Be Misleading
BMI measures weight relative to height. It does not distinguish between muscle and fat, and it says nothing about where your body stores fat. A muscular athlete with very little body fat can land in the overweight or even obese range on a BMI chart, while an older adult with low muscle mass and a high percentage of body fat might register a “normal” BMI. Both readings are technically wrong about the person’s actual health risk.
The American Diabetes Association’s 2025 Standards of Care make this explicit: BMI is “at most an imperfect measure of adipose tissue mass” and “does not measure adipose tissue distribution or function.” Their current recommendation is that a diagnosis of obesity should be based on an overall assessment that includes how much fat you carry, where it’s distributed, and whether it’s already causing metabolic, physical, or psychological consequences. BMI is a starting point, not a verdict.
Measurements That Fill the Gaps
Waist circumference is one of the most practical supplements to BMI because belly fat, the kind packed around your internal organs, is more closely linked to heart disease and diabetes than fat stored in your hips or thighs. The National Heart, Lung, and Blood Institute considers a waist larger than 35 inches in women or 40 inches in men a marker of higher risk for heart disease and type 2 diabetes. Research published by the American Heart Association found that waist size actually predicts heart attacks better than BMI, particularly in women.
Other useful measures include waist-to-hip ratio, waist-to-height ratio, and body composition testing that estimates your actual percentage of fat versus muscle. Your doctor may also look at blood pressure, blood sugar, cholesterol, and other metabolic markers. Two people with identical BMIs can have very different risk profiles depending on these factors. If your BMI is in the overweight or Class I range but your waist circumference, blood work, and blood pressure are all normal, your actual risk may be lower than the number suggests. The reverse is also true: a BMI in the “normal” range doesn’t guarantee metabolic health, especially if you carry excess fat around your midsection.