BMI or BRI? How to Assess Your Body Weight

When Arnold Schwarzenegger was Mr. Universe, at 6’2” and 235 pounds, he had a body mass index (BMI) of 30.2—a number that would classify him as “obese.” But with a waist circumference of less than 34 inches, the bodybuilder had a body roundness index (BRI) of just 2.6, which classified him as “very lean.”

“He had a miniscule waist and a massive amount of muscle,” says Wajahat Mehal, MD, director of the Yale Metabolic Health & Weight Loss Program. “In certain extremes, if you look at one of these numbers alone, you might mistakenly think a person is very healthy—or not—depending on their body composition.”

For most people, however, both the BMI and BRI assessment tools will provide similar results. But if you’re looking for a verdict on your overall health, using one—or even both—of these numbers isn’t entirely reliable.

“This is one data point about a person’s health, but it doesn’t tell you everything,” Dr. Mehal says. “It’s an important metric that should be considered along with everything else, like blood pressure, blood glucose, and cholesterol.”

Your weight is a key metric of your overall metabolic health—or your body’s ability to process food into energy. Because both BMI and BRI indicate whether you’re at a healthy weight, these tools can give doctors a general idea of your risk for heart disease, stroke, diabetes, and other chronic conditions.

But while both of these body indices are measures of healthy weight range, they arrive at their conclusions in different ways

BMI is derived from your height and weight, but it says nothing of how that weight is distributed. BRI, on the other hand, is based on your height and your waist circumference, which might be a better indicator of whether the extra weight someone is carrying is mostly fat or mostly muscle.

The potential advantages of using BRI as a screening tool were suggested in a study involving nearly 33,000 adults and published in JAMA Network Open in 2024. During a 19-year period, those with the lowest BRI and the highest BRI were the most likely to die at any time from any cause. The study findings indicate that the index could be a reliable measure of dangerously unhealthy weight on both sides of the scale.

BMI, on the other hand, may have a larger margin of error. While bodybuilders and pro athletes, for example, might have an inflated BMI, some people on the other end of the spectrum might have a misleadingly low BMI.

For example, someone could have a healthy BMI, but an unhealthy BRI. “This could be an older gentleman who’s lost most of his muscle and has skinny arms and legs, but has a potbelly,” Dr. Mehal says. “Because he doesn’t have much mass anywhere else in his body, his overall weight isn’t very high.” So in this scenario, BMI would not identify a person who has health risks due to his waist circumference, while his BRI would raise a red flag, he adds.

While these are extreme examples, there are other people in the general population who might not be well served by the BMI metric either. Asian people, older adults, and women typically have more body fat at a lower BMI than their respective white, younger, or male counterparts. BMI doesn’t account for race, age, and gender, though these factors do play a role in fat distribution. In fact, the BMI cut-offs between underweight, healthy weight, overweight, and obesity were based entirely on large cohorts of non-Hispanic white people.

For all these reasons, the American Medical Association recently encouraged physicians to use a second measure of body fat, such as the body adiposity index, relative fat mass, or waist circumference, in conjunction with BMI to determine whether the number on the scale is a healthy one.

All of that said, BMI alone still gets it right for most people, says Dr. Mehal. In a study published in 2025 in JAMA, researchers analyzed data on 2,225 adults of different races under age 60. Based on BMI alone, 39.7% of them would be considered obese. Nearly all of those who were considered obese based on BMI alone—98% of them—also met the criteria for obesity by a second measure, such as BRI or a scan to directly measure body fat. BMI missed the mark for just 2% of the people it classified as obese.

Luckily, easy-to-use calculators for BMI and BRI can be found online. But for those who want to work these numbers out on paper themselves, here are the formulas.

BMI equation = weight (kilograms)/height (meters)²

Here’s what your BMI means:

• <18.5 = underweight

• 18.5 to 24.9 = healthy weight

• 25 to 29.9 = overweight

• >29.9 = obesity

Even the low end of overweight is not a good sign, explains Dr. Mehal. “Many people know that a BMI over 30 is considered too high. The data is very clear, but the range between 25 and 30 is not a healthy place to be either,” he says.

The BRI equation is more complicated.

BRI = 364.2 − 365.5 × √ (1 − [waist circumference in centimeters / 2ℼ]² / [0.5 × height in centimeters]²)

Here’s what your BRI means:

• <3.41 = very lean

• 3.41 to 4.45 = lean to average

• 4.45 to 5.46 = average

• 5.46 to 6.91 = above average

• >6.91 = high

If your BMI or BRI is not in the healthy range, consider the full picture of your health, suggests Dr. Mehal.

“In the same way that you can be pretty healthy even with a slightly high blood pressure, you can be pretty healthy with a slightly high BMI or BRI, too,” he says.

In an annual physical, most doctors continue to consider your BMI and view that result alongside several other important numbers. These include your blood pressure, blood sugar, cholesterol, and other key figures.

Still, if one of these body indices is skewing on the higher end, talk about it. Your doctor can help.

“Just as you would bring up a headache or back pain with your doctor, people should feel comfortable bringing this up with their health care providers,” says Dr. Mehal. A doctor can evaluate factors besides diet and exercise—such as your medications and sleeping habits—that may be contributing to your weight.