BMI Calculator
Use this free BMI (Body Mass Index) calculator to check if your weight is healthy for your height. BMI is a useful screening tool that can indicate whether you're underweight, at a healthy weight, overweight, or obese.
How to Calculate BMI
BMI Formula
Body Mass Index (BMI) is calculated using your weight and height. The formula differs slightly depending on the unit system you're using.
BMI = 70 / (1.7 × 1.7) = 70 / 2.89 = 24.22
BMI = 703 × 154 / (67 × 67) = 108,262 / 4,489 = 24.12
BMI Categories
BMI values are categorized into different weight status groups:
- Underweight: BMI less than 18.5
- Normal weight: BMI 18.5 to 24.9
- Overweight: BMI 25 to 29.9
- Obesity (Class 1): BMI 30 to 34.9
- Obesity (Class 2): BMI 35 to 39.9
- Obesity (Class 3): BMI 40 or higher
These categories are the same for men and women of all body types and ages. However, BMI may be interpreted differently for children and teens, athletes, older adults, and pregnant women.
Understanding BMI
What BMI Tells You
BMI is a screening tool that can indicate whether a person has a healthy weight for their height. It's commonly used to identify potential weight problems in adults and is a simple, inexpensive method for categorizing weight status.
A high BMI can indicate high body fatness, while a low BMI can indicate too low body fatness. BMI correlates with various health outcomes, including cardiovascular disease, type 2 diabetes, hypertension, and certain cancers.
Limitations of BMI
While BMI is a useful screening tool, it does have several limitations:
- It doesn't distinguish between fat and muscle mass. Athletes with high muscle mass may have a high BMI but low body fat.
- It doesn't account for where fat is stored. Abdominal fat (around the waist) poses more health risks than fat stored in other areas.
- It may not be as accurate for elderly individuals who have lost muscle mass.
- It doesn't consider differences in body composition between different ethnic groups.
- It doesn't account for gender differences in body composition.
Because of these limitations, BMI should be used as one of several tools to assess health, not as the sole determinant.
Beyond BMI: Other Health Indicators
For a more comprehensive health assessment, consider these additional measurements alongside BMI:
- Waist circumference: Measures abdominal fat, which is a risk factor for heart disease and type 2 diabetes.
- Waist-to-hip ratio: Compares waist circumference to hip circumference, indicating fat distribution.
- Body fat percentage: Directly measures the proportion of fat in your body.
- Blood pressure, cholesterol, and blood sugar levels: Important indicators of metabolic health.
- Fitness level: Cardiovascular fitness and strength are important health indicators regardless of weight.
Frequently Asked Questions
Is BMI accurate for everyone?
BMI is not equally accurate for all individuals. It may overestimate body fat in athletes and others with muscular builds, and it may underestimate body fat in older persons and others who have lost muscle mass. Additionally, BMI may not be as accurate for certain ethnic groups who may have different body compositions at the same BMI levels. For example, some Asian populations may have higher body fat percentages at lower BMI values compared to Caucasian populations.
How often should I check my BMI?
For most adults, checking BMI once or twice a year is sufficient, typically during regular health check-ups. If you're actively trying to lose or gain weight, you might want to check your BMI more frequently, perhaps every 1-3 months, to track your progress. However, it's important not to become overly focused on the number. BMI is just one health indicator, and small fluctuations are normal. Focus on overall health trends rather than day-to-day changes.
What should I do if my BMI indicates I'm overweight or obese?
If your BMI indicates you're overweight or obese, it's advisable to consult with a healthcare provider for a more comprehensive health assessment. They can help determine if your weight is affecting your health and provide personalized recommendations. Generally, gradual weight loss through a balanced diet and regular physical activity is recommended for those who need to lose weight. Aim for sustainable lifestyle changes rather than quick fixes or extreme diets. Remember that even modest weight loss (5-10% of your total body weight) can lead to significant health improvements.
Is BMI different for children and teens?
Yes, BMI is calculated the same way for children and teens as it is for adults, but it's interpreted differently. For children and teens (aged 2-20), BMI is age- and sex-specific and is often referred to as "BMI-for-age." Instead of fixed categories, children's BMI values are compared to percentiles based on growth charts that account for normal differences in body fat between boys and girls and at different ages. For example, a child might be classified as overweight if their BMI is at or above the 85th percentile and below the 95th percentile for children of the same age and sex.
Can I have a normal BMI but still be unhealthy?
Yes, it's possible to have a normal BMI but still have health issues. This condition is sometimes referred to as "normal weight obesity" or being "skinny fat." It occurs when a person has a normal BMI but has a high percentage of body fat relative to lean muscle mass. These individuals may face similar health risks as those who are visibly overweight, including increased risk for metabolic syndrome, cardiovascular disease, and other obesity-related conditions. Conversely, it's also possible to have an overweight or obese BMI classification but be metabolically healthy, particularly if you're physically active and have good cardiovascular fitness.