Calculate your Body Mass Index (BMI) to assess if your weight is healthy for your height.
BMI is a screening tool and does not account for muscle mass, bone density, or overall body composition.
Body Mass Index (BMI) is a numerical value calculated from your weight and height. Developed by Belgian mathematician Adolphe Quetelet in the 1830s, it provides a simple screening tool to assess whether your weight falls within a healthy range for your height.
BMI is widely used by healthcare providers, insurance companies, and public health organizations because it's quick to calculate and requires only two measurements. However, it's important to understand both its usefulness and its limitations.
The BMI formula divides weight by the square of height:
For imperial units (pounds and inches), a conversion factor of 703 is applied:
The World Health Organization (WHO) defines these standard BMI categories for adults:
| BMI Range | Category | Health Risk |
|---|---|---|
| Below 16.0 | Severe thinness | High |
| 16.0 – 16.9 | Moderate thinness | Moderate |
| 17.0 – 18.4 | Mild thinness | Low |
| 18.5 – 24.9 | Normal weight | Average |
| 25.0 – 29.9 | Overweight | Increased |
| 30.0 – 34.9 | Obese Class I | High |
| 35.0 – 39.9 | Obese Class II | Very high |
| 40.0 and above | Obese Class III | Extremely high |
For a person who is 5'9" (69 inches) and weighs 150 lbs:
This falls in the "Normal weight" category.
For someone 170 cm tall weighing 80 kg:
This falls in the "Overweight" category.
Being underweight can indicate malnutrition or underlying health conditions. Associated risks include:
This range is associated with the lowest statistical health risks. However, BMI alone doesn't guarantee good health—diet quality, physical activity, and other factors matter significantly.
Carrying excess weight increases risk for:
Obesity significantly increases risk for multiple conditions:
BMI is calculated the same way for children, but interpreted differently. Because body composition changes with age and differs between boys and girls, children's BMI is expressed as a percentile compared to other children of the same age and sex.
| Percentile | Category |
|---|---|
| Below 5th | Underweight |
| 5th to 84th | Healthy weight |
| 85th to 94th | Overweight |
| 95th and above | Obese |
The CDC provides growth charts for tracking children's BMI percentiles from ages 2 to 20. A child's BMI percentile indicates how their BMI compares to other children of the same age and sex in a reference population.
Different populations have varying health risk profiles at the same BMI. Some countries and organizations use modified thresholds:
Research shows that Asian populations tend to have higher body fat percentages and greater health risks at lower BMI values. Many Asian countries use:
| BMI Range | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 22.9 | Normal |
| 23.0 – 24.9 | Overweight (At Risk) |
| 25.0 – 29.9 | Obese Class I |
| 30.0 and above | Obese Class II |
Genetic, dietary, and lifestyle factors contribute to different body compositions across populations. Asian individuals may develop:
This doesn't mean standard BMI is "wrong"—it's a statistical tool that works better for some populations than others.
BMI is a screening tool, not a diagnostic measure. Understanding its limitations helps you interpret your results appropriately.
BMI cannot distinguish between:
A bodybuilder and a sedentary person can have identical BMI with vastly different health profiles.
Where fat is stored matters more than total amount. Visceral fat (around organs in the abdomen) carries significantly higher health risks than subcutaneous fat (under the skin) or fat stored in the hips and thighs.
Two people with identical BMI can have very different risk profiles based on where they carry their weight.
BMI categories don't adjust for:
Some research suggests that for certain conditions (heart failure, kidney disease, some cancers), slightly overweight patients may have better outcomes than normal-weight patients. This doesn't mean being overweight is healthy—it may reflect other factors like muscle mass or nutritional reserves.
For a more complete picture of health, consider these additional measurements:
Measures abdominal fat specifically. Measure at the narrowest point between ribs and hip bones.
High risk thresholds:
Divide waist measurement by hip measurement.
High risk thresholds:
Divide waist measurement by height. This simple metric works across different populations.
Directly measures fat vs. lean mass. Healthy ranges vary by age and sex:
| Category | Men | Women |
|---|---|---|
| Essential fat | 2-5% | 10-13% |
| Athletes | 6-13% | 14-20% |
| Fitness | 14-17% | 21-24% |
| Average | 18-24% | 25-31% |
| Obese | 25%+ | 32%+ |
Methods include:
A newer metric that combines height and waist circumference to estimate body fat percentage and visceral fat. Some research suggests it predicts health risks better than BMI alone.
Healthcare providers use BMI as one data point among many. A clinical assessment typically includes:
BMI alone doesn't diagnose anything—it flags potential concerns for further evaluation.
Consider consulting a healthcare provider if:
Regardless of your current BMI, focus on sustainable health practices:
Chronic stress can:
Consider meditation, exercise, social connection, or professional support.
Sustainable habits beat aggressive short-term approaches. Small, consistent changes maintained over time produce lasting results.
BMI often overestimates body fat in athletes and people with high muscle mass. A football player or bodybuilder might have an "obese" BMI with very low body fat. For athletes, body fat percentage and waist circumference are more useful metrics.
BMI itself is just a calculation that doesn't change—but what's "healthy" may shift. Older adults naturally lose muscle and gain fat, so the same BMI at 70 may represent more body fat than at 30. Some researchers suggest slightly higher BMI (25-27) may be acceptable for older adults.
Yes. "Normal weight obesity" describes people with normal BMI but high body fat percentage, often due to low muscle mass and sedentary lifestyle. They may have metabolic syndrome, high blood pressure, or elevated blood sugar despite normal BMI.
The BMI calculation and categories are the same, but body composition differs. Women naturally have higher body fat percentages than men. A woman and man with identical BMI likely have different amounts of body fat.
BMI is cheap, easy to calculate, and statistically correlates with health outcomes at the population level. It's not perfect for individuals, but it's practical for large-scale risk assessment. Some insurers also consider waist circumference or other factors.
Most health organizations recommend 1-2 pounds (0.5-1 kg) per week for sustainable weight loss. Faster loss often means losing muscle along with fat and is harder to maintain long-term.
Yes, significantly. Abdominal fat (apple shape) carries higher risks than hip/thigh fat (pear shape). Waist circumference or waist-to-hip ratio captures this better than BMI.
Yes. BMI below 18.5 is considered underweight and carries health risks including weakened immunity, bone loss, fertility problems, and nutritional deficiencies. BMI below 16 indicates severe thinness requiring medical attention.