Global Obesity Rates
Tap or hover a country to see its adult obesity rate (BMI ≥ 30)
How BMI Is Calculated
BMI divides your weight in kilograms by the square of your height in meters. The formula is simple: weight (kg) / height (m)². In imperial units, the equivalent is weight (lbs) × 703 / height (in)². The result places you into one of several categories that indicate whether your weight falls within, above, or below the range statistically associated with the lowest health risks for your height.
The index was developed by Belgian mathematician Adolphe Quetelet in the 1830s as a population-level statistical tool. It was never designed to diagnose individual health, and that distinction still matters. BMI works well as a quick screening metric for large groups, but it tells you nothing about body composition, fat distribution, or metabolic health on its own.
BMI Categories and Health Risk
| BMI | Classification | Associated Risk Level |
|---|---|---|
| Below 18.5 | Underweight | Nutritional deficiency, weakened immunity, bone density loss |
| 18.5 – 24.9 | Normal weight | Lowest statistical risk for weight-related conditions |
| 25.0 – 29.9 | Overweight | Increased risk for type 2 diabetes, hypertension, cardiovascular disease |
| 30.0 – 34.9 | Obese (Class I) | Moderate to high risk of weight-related health problems |
| 35.0 – 39.9 | Obese (Class II) | High risk of serious health conditions including sleep apnea and joint problems |
| 40.0+ | Obese (Class III) | Very high risk requiring comprehensive medical attention |
These thresholds come from the World Health Organization and are used internationally by healthcare systems. They’re based on large-scale epidemiological data linking BMI ranges to disease incidence and mortality rates across populations.
Where BMI Falls Short
BMI has well-documented limitations that are worth knowing before you draw conclusions from your result.
Muscle vs. Fat
BMI treats all mass equally. A 6-foot, 220-pound rugby player and a sedentary person of the same dimensions get the same BMI, despite radically different body compositions. Athletes, weightlifters, and anyone with above-average muscle mass will often register as “overweight” while having low body fat.
Ethnicity
Research shows that health risks associated with specific BMI values differ across ethnic groups. People of South Asian, Chinese, and Japanese descent tend to carry higher body fat percentages at lower BMIs. Some health organizations in Asia use 23 rather than 25 as the overweight threshold.
Age and Sex
Body composition shifts naturally with age. Older adults tend to have less muscle and more fat at the same BMI compared to younger adults. Women generally carry more body fat than men at equivalent BMI values. The standard thresholds don’t adjust for either.
Fat Distribution
Where you carry fat matters more than how much you carry. Visceral fat around the abdomen is strongly linked to metabolic syndrome, heart disease, and type 2 diabetes. Two people with identical BMIs can have vastly different risk profiles based on fat distribution alone.
None of these limitations mean BMI is useless. It means BMI works best as a starting point, not a final answer. Used alongside other measurements, it contributes to a more complete picture of health.
Metrics That Add Context to Your BMI
If you want a more accurate read on your weight-related health, these measurements complement BMI well. None require specialized equipment.
Getting Accurate Measurements
Small measurement errors can shift your BMI by a full point or more, which may move you across category boundaries. A few practices help ensure consistency.
For height, stand against a flat wall without shoes. Keep your head level with your eyes looking straight ahead (the Frankfort plane). Have someone else place a flat object on your head and mark the wall, then measure to the mark. Height measured at a doctor’s office with a stadiometer is the most reliable.
For weight, weigh yourself at the same time each day, ideally in the morning after using the bathroom and before eating. Wear similar clothing each time and use the same scale. Daily weight fluctuates by 2–5 pounds from water retention, meal timing, and other factors, so a weekly average is more meaningful than any single reading.
Practical Steps Based on Your Result
BMI Below 18.5
Focus on calorie-dense, nutrient-rich foods rather than empty calories. Nuts, avocados, whole grains, and protein sources help build mass in a healthy way. Add resistance training 2–3 times weekly to build muscle. If gaining weight is consistently difficult, ask your doctor to check for thyroid conditions, celiac disease, or other underlying causes.
BMI 18.5 – 24.9
Maintain what’s working. Aim for at least 150 minutes of moderate activity per week, eat a balanced diet with adequate protein, and keep an eye on waist circumference as you age. Even within the normal range, improvements in fitness and nutrition continue to lower disease risk.
BMI 25 – 29.9
A sustained calorie deficit of 250–500 calories per day produces 0.5–1 pound of fat loss per week. Combine dietary changes with increased physical activity. Measure your waist circumference to assess central fat distribution, which is a stronger predictor of health risk than BMI alone in this range.
BMI 30+
Work with a healthcare provider to develop a realistic, gradual plan. Losing just 5–10% of body weight can substantially improve blood pressure, blood sugar, and cholesterol levels. Set process goals (daily walks, meal prep, sleep hygiene) rather than just outcome goals, and monitor blood pressure and blood sugar alongside weight.
BMI in Children and Adolescents
Standard adult BMI categories don’t apply to anyone under 18. Children and teens are assessed using age and sex-specific BMI percentile charts, because healthy body fat levels change substantially as they grow. A child at the 85th percentile for their age and sex is classified as overweight; the 95th percentile and above is considered obese. Pediatricians track BMI-for-age over time on growth charts to identify concerning trends rather than relying on single measurements.
The “Obesity Paradox”
Some research has found that people in the overweight BMI range (25–29.9) may actually have equal or even lower mortality rates than those in the normal range in certain contexts, particularly among older adults and people with chronic conditions like heart failure. This has been called the “obesity paradox” and has sparked significant debate in medical literature.
Several factors may explain the finding: people with chronic illness who lose weight unintentionally appear “normal weight” but are actually sicker, extra weight may provide metabolic reserves during illness, and muscle mass can push BMI up while actually being protective. The takeaway isn’t that being overweight is healthy, but that BMI alone is a blunt instrument for predicting individual health outcomes.
When to Talk to a Doctor
Your BMI result alone is not a diagnosis. But certain situations warrant a conversation with a healthcare provider: a BMI below 16 or above 35, difficulty gaining or losing weight despite consistent effort, a BMI in the normal range combined with a waist circumference above the thresholds mentioned earlier, or any BMI result paired with symptoms like fatigue, joint pain, shortness of breath, or blood sugar issues.
A doctor can order blood work (fasting glucose, lipid panel, HbA1c) that tells you far more about your metabolic health than BMI does. They can also assess body composition, check blood pressure, and evaluate your personal and family health history in context.