BMI is a quick screening number based on height and weight, but it cannot tell fat from muscle or show where fat sits. Waist size and waist-to-height ratio add information about abdominal fat, and body fat measures fill in the rest. Used together, they give a clearer picture.
BMI, waist size and body fat percentage each measure something different. BMI compares weight to height and works well as a quick screen across large groups, but it cannot separate fat from muscle or show where fat is stored. Waist circumference and waist-to-height ratio estimate fat around the abdomen, which carries more health risk, and body fat measurements show how much of your weight is fat. Most experts now recommend using BMI alongside at least one of the others rather than on its own.
| Measure | What it tells you | Main limitation |
|---|---|---|
| BMI | Weight relative to height | Does not distinguish fat from muscle or show fat distribution |
| Waist circumference | Fat carried around the abdomen | Single cutoffs do not fit every age, sex or ethnicity equally |
| Waist-to-height ratio | Abdominal fat scaled to your height | NICE applies its cutoffs to people with a BMI under 35 |
| Body fat percentage | Share of your weight that is fat | Requires a measuring device or scan, which is not always available |
Each one answers a slightly different question, which is why they work best together.
BMI is weight in kilograms divided by height in meters squared. You can calculate yours with our BMI calculator. The CDC uses these adult categories:
| BMI | Category |
|---|---|
| Under 18.5 | Underweight |
| 18.5 to under 25 | Healthy weight |
| 25 to under 30 | Overweight |
| 30 to under 35 | Class 1 obesity |
| 35 to under 40 | Class 2 obesity |
| 40 or higher | Class 3 (severe) obesity |
The CDC describes BMI as a screening measure and "one potential health indicator" that "should be considered with other factors when assessing an individual's health." For adults 20 and older, the same categories apply regardless of age, sex or race.
A 2008 study in the International Journal of Obesity compared BMI with estimated body fat (measured by bioelectrical impedance) in 13,601 adults from a national US survey. Using body fat above 25 percent for men and 35 percent for women as the reference for obesity:
BMI performed worse with age, and in the 25 to 29.9 range it could not distinguish between body fat and lean mass in either sex.
In 2023, the American Medical Association adopted policy describing BMI as an imperfect way to measure body fat because it does not account for differences across race and ethnic groups, sexes, genders and age. The AMA noted that BMI was based primarily on data from earlier generations of non-Hispanic white populations, and that it correlates with fat mass across populations but "loses predictability" for individuals. The policy recommends using BMI together with other measures such as waist circumference, body composition, visceral fat and metabolic factors.
A 2004 World Health Organization expert consultation published in The Lancet found that the share of Asian people at high risk of type 2 diabetes and cardiovascular disease is substantial at BMIs below 25. The point where risk rises varied from 22 to 25 across Asian populations. The WHO kept its international cutoffs but identified additional public health action points at 23, 27.5, 32.5 and 37.5. NICE in the UK similarly recommends lower BMI thresholds for people of South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean family background.
Fat stored around the abdomen is more closely tied to health risk than fat on the hips. NHLBI notes that people who carry fat mainly around the waist have a higher risk of heart disease and type 2 diabetes, and that a waist of more than 35 inches for women or more than 40 inches for men increases risk.
NHLBI's measuring method is to wrap a tape just above the hipbones and read it just after breathing out. Our article on visceral fat explains why abdominal fat matters and what reduces it.
The UK's National Institute for Health and Care Excellence (NICE) added waist-to-height ratio to its obesity guideline in 2022. Its advice is to keep your waist to less than half your height.
NICE describes this method:
| Waist-to-height ratio | NICE classification |
|---|---|
| 0.4 to 0.49 | Healthy central adiposity, no increased risk |
| 0.5 to 0.59 | Increased central adiposity, increased risk |
| 0.6 or more | High central adiposity, further increased risk |
NICE says these classifications can be used for people with a BMI under 35, of both sexes and all ethnicities, including adults with high muscle mass. Note that NICE and NHLBI describe slightly different tape positions, so pick one and use it consistently.
Body fat percentage measures how much of your weight is fat. The 2025 Lancet commission on clinical obesity recommended that excess body fat be confirmed "by either direct measurement of body fat, where available, or at least one anthropometric criterion (eg, waist circumference, waist-to-hip ratio, or waist-to-height ratio) in addition to BMI." It added that at a BMI above 40, excess body fat can be assumed without further confirmation.
Body fat can be estimated in several ways, including bioelectrical impedance, the method used in the 2008 accuracy study above. Methods differ, so if you track body fat, using the same method each time keeps your comparisons consistent.
Not always. Because BMI uses only height and weight, it cannot tell muscle from fat. The 2008 study found that in the 25 to 29.9 range, BMI could not distinguish body fat from lean mass, which is one reason NICE says waist-to-height ratio can be used in adults with high muscle mass.
NHLBI flags higher risk above 35 inches for women and above 40 inches for men. NICE recommends a waist less than half your height. Both are screening guides, and a licensed provider can interpret them alongside your other health information.
No, but it works best as one number among several. The CDC, AMA and the 2025 Lancet commission all describe BMI as a starting point that should be combined with other measures, such as waist size, when assessing an individual.
Many people track weight, waist size or both. Waist measurements can show changes in abdominal fat that the scale may not reflect, especially if you are also building muscle. Measure the same way, at the same time of day, for the most reliable trend.
These numbers are screening tools, not diagnoses. A licensed provider can combine your BMI, waist measurement, lab results and health history to understand your risk and discuss whether any treatment is appropriate. You can read more about why obesity is treated as a chronic disease. This article is educational and does not determine eligibility for any treatment.
Written by the NewDay Wellness editorial team from the sources above and checked against them before publication, and medically reviewed by Dr. Sean Arora and Dr. Shannon Arora of Arora Health & Aesthetics; see our editorial standards. This article is educational and does not diagnose conditions, establish eligibility for any medication, or replace care from a licensed provider. Compounded medications are not FDA-approved.
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