The most common way to check if you’re obese is by calculating your body mass index, or BMI. A BMI of 30 or higher falls into the obesity range for most adults. But BMI is just one piece of the puzzle, and newer approaches look at where you carry fat, how much of your weight is actually fat, and whether your metabolic health is affected.
How to Calculate Your BMI
BMI is your weight in kilograms divided by your height in meters squared. If you prefer pounds and inches, multiply your weight in pounds by 703, then divide by your height in inches squared. You can also use any free online BMI calculator to skip the math entirely.
For adults 20 and older, the CDC defines the categories like this:
- Underweight: below 18.5
- Healthy weight: 18.5 to 24.9
- Overweight: 25 to 29.9
- Class 1 obesity: 30 to 34.9
- Class 2 obesity: 35 to 39.9
- Class 3 (severe) obesity: 40 or higher
To put this in practical terms, a person who is 5’9″ would cross into the obesity range at roughly 203 pounds. Someone 5’4″ would reach it at about 175 pounds.
Why BMI Doesn’t Tell the Whole Story
BMI treats all weight the same. It can’t distinguish between fat, muscle, and bone mass. It also can’t tell you what type of fat you have or where on your body you carry it. A muscular person can easily land in the “obese” BMI range while carrying very little body fat. Conversely, someone with a normal BMI can carry a disproportionate amount of fat around their organs, which carries real health risks.
Ethnicity also changes the picture significantly. The WHO recommends lower cutoffs for Asian populations: a BMI of 23 for overweight and 27.5 for obesity, compared to the standard 25 and 30. This is because people of Asian descent tend to develop obesity-related health problems at lower BMIs. If you’re of South Asian, East Asian, or Southeast Asian descent, the standard BMI chart may underestimate your risk.
Body Fat Percentage as a Better Measure
Because BMI is just a ratio of weight to height, many clinicians now look at body fat percentage for a more accurate picture. A 2025 study using US national survey data defined obesity as a body fat percentage of at least 30% for men and 42% for women. The overweight threshold was 25% for men and 36% for women.
There are several ways to measure body fat. DEXA scans, which use low-dose X-rays, are considered the gold standard for accuracy. They show exactly how much of your body is fat, muscle, and bone, and where each is distributed. The downside is cost: DEXA scans typically run $75 to $200 out of pocket and require a visit to a clinic or imaging center.
Bioelectrical impedance analysis, or BIA, is the technology built into many bathroom scales and handheld devices. It sends a small electrical current through your body and estimates fat based on how quickly the signal travels. Research comparing BIA to DEXA scans shows good agreement between the two methods, making BIA a reasonable option for tracking changes over time at home. It’s less precise on any single reading, though, and can be thrown off by hydration levels, recent exercise, or a full stomach.
Waist Circumference: A Simple Check
Where you carry fat matters as much as how much you carry. Fat stored around your midsection, often called visceral fat, wraps around internal organs and drives up risk for heart disease, type 2 diabetes, and stroke far more than fat stored in your hips or thighs.
You can check this at home with a tape measure. Wrap it around your bare waist just above your hip bones, keeping it snug but not compressing the skin, and measure after a normal exhale. For men, a waist circumference above 40 inches signals elevated health risk. For women, the threshold is 35 inches. This single measurement, combined with your BMI, gives you a much clearer picture than either number alone.
What Your Blood Work Reveals
Not everyone with a high BMI develops the metabolic problems typically linked to obesity. Clinicians look at a set of markers to assess whether excess weight is actively affecting your health. The key ones are fasting blood sugar at or above 100 mg/dL, blood pressure at or above 130/85, elevated triglycerides (a type of blood fat) at or above 150 mg/dL, and low HDL cholesterol (below 40 mg/dL for men, below 50 for women).
Having two or more of these markers alongside excess body fat signals that obesity is creating metabolic harm. Having fewer than two is sometimes described as “metabolically healthy obesity,” though that term is somewhat misleading. Long-term studies suggest that even without current metabolic problems, carrying significant excess fat increases the likelihood of developing them over time. Still, these markers help you and your doctor prioritize what needs attention first.
How Obesity Is Assessed in Children
For children and teens ages 2 through 19, BMI works differently. Because kids are still growing, their BMI is compared against growth charts for their age and sex. A child at or above the 95th percentile for their age group is considered obese. This means their BMI is higher than 95% of children the same age and sex. Your pediatrician calculates this at routine checkups, so you don’t need to interpret the percentile charts yourself.
Putting the Numbers Together
No single number definitively tells you whether you’re obese. The most complete self-assessment combines three things: your BMI, your waist circumference, and any metabolic symptoms you’re aware of (like high blood pressure or elevated blood sugar from past lab work). If your BMI is 30 or above, your waist exceeds the thresholds, and you have metabolic markers that are off, those three signals together paint a clear picture.
If your BMI is borderline, say in the 27 to 32 range, context matters more. A person with a muscular build may have a BMI of 31 with a healthy waist measurement and normal blood work. Someone else at 28 could carry most of their weight around the midsection and already show elevated blood sugar. The clinical world is increasingly moving toward what some professional organizations call “adiposity-based chronic disease,” which focuses less on the number on the scale and more on whether excess body fat is causing measurable health problems. A standard blood panel and a tape measure can tell you a lot before you ever step on a DEXA scanner.